## Issue Addressed
Upgrade libp2p to v0.52
## Proposed Changes
- **Workflows**: remove installation of `protoc`
- **Book**: remove installation of `protoc`
- **`Dockerfile`s and `cross`**: remove custom base `Dockerfile` for cross since it's no longer needed. Remove `protoc` from remaining `Dockerfiles`s
- **Upgrade `discv5` to `v0.3.1`:** we have some cool stuff in there: no longer needs `protoc` and faster ip updates on cold start
- **Upgrade `prometheus` to `0.21.0`**, now it no longer needs encoding checks
- **things that look like refactors:** bunch of api types were renamed and need to be accessed in a different (clearer) way
- **Lighthouse network**
- connection limits is now a behaviour
- banned peers no longer exist on the swarm level, but at the behaviour level
- `connection_event_buffer_size` now is handled per connection with a buffer size of 4
- `mplex` is deprecated and was removed
- rpc handler now logs the peer to which it belongs
## Additional Info
Tried to keep as much behaviour unchanged as possible. However, there is a great deal of improvements we can do _after_ this upgrade:
- Smart connection limits: Connection limits have been checked only based on numbers, we can now use information about the incoming peer to decide if we want it
- More powerful peer management: Dial attempts from other behaviours can be rejected early
- Incoming connections can be rejected early
- Banning can be returned exclusively to the peer management: We should not get connections to banned peers anymore making use of this
- TCP Nat updates: We might be able to take advantage of confirmed external addresses to check out tcp ports/ips
Co-authored-by: Age Manning <Age@AgeManning.com>
Co-authored-by: Akihito Nakano <sora.akatsuki@gmail.com>
## Issue Addressed
NA
## Proposed Changes
Carries on from #4115, with the following modifications:
1. Self-hosted runners are only enabled if `github.repository == sigp/lighthouse`.
- This allows forks to still have Github-hosted CI.
- This gives us a method to switch back to Github-runners if we have extended downtime on self-hosted.
1. Does not remove any existing dependency builds for Github-hosted runners (e.g., installing the latest Rust).
1. Adds the `WATCH_HOST` environment variable which defines where we expect to find the postgres db in the `watch` tests. This should be set to `host.docker.internal` for the tests to pass on self-hosted runners.
## Additional Info
NA
Co-authored-by: antondlr <anton@delaruelle.net>
## Issue Addressed
Speed up CI by installing foundry with Github action instead of building Anvil from source.
Building anvil from source on GItHub hosted runners currently takes about 10 mins. Using the `foundry-toolchain` action to install only takes about 2 seconds.
## Issue Addressed
Workaround for https://github.com/foundry-rs/foundry/issues/5115.
## Proposed Changes
Allow Anvil to be installed on Windows without errors by enabling the IPC features (which we don't use, but Anvil expects to exist).
## Issue Addressed
N/A
## Proposed Changes
Modifies the local testnet scripts to start a network with genesis validators embedded into the genesis state. This allows us to start a local testnet without the need for deploying a deposit contract or depositing validators pre-genesis.
This also enables us to start a local test network at any fork we want without going through fork transitions. Also adds scripts to start multiple geth clients and peer them with each other and peer the geth clients with beacon nodes to start a post merge local testnet.
## Additional info
Adds a new lcli command `mnemonics-validators` that generates validator directories derived from a given mnemonic.
Adds a new `derived-genesis-state` option to the `lcli new-testnet` command to generate a genesis state populated with validators derived from a mnemonic.
## Issue Addressed
N/A
## Proposed Changes
Replace ganache-cli with anvil https://github.com/foundry-rs/foundry/blob/master/anvil/README.md
We can lose all js dependencies in CI as a consequence.
## Additional info
Also changes the ethers-rs version used in the execution layer (for the transaction reconstruction) to a newer one. This was necessary to get use the ethers utils for anvil. The fixed execution engine integration tests should catch any potential issues with the payload reconstruction after #3592
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
## Issue Addressed
The latest stable version (1.69.0) of Rust was released on 20 April and contains this change:
- [Update the minimum external LLVM to 14.](https://github.com/rust-lang/rust/pull/107573/)
This impacts some of our CI workflows (build and release-test-windows) that uses LLVM 13.0. This PR updates the workflows to install LLVM 15.0.
**UPDATE**: Also updated `h2` to address [this issue](https://github.com/advisories/GHSA-f8vr-r385-rh5r)
## Issue Addressed
There was a [`VecDeque` bug](https://github.com/rust-lang/rust/issues/108453) in some recent versions of the Rust standard library (1.67.0 & 1.67.1) that could cause Lighthouse to panic (reported by `@Sea Monkey` on discord). See full logs below.
The issue was likely introduced in Rust 1.67.0 and [fixed](https://github.com/rust-lang/rust/pull/108475) in 1.68, and we were able to reproduce the panic ourselves using [@michaelsproul's fuzz tests](https://github.com/michaelsproul/lighthouse/blob/fuzz-lru-time-cache/beacon_node/lighthouse_network/src/peer_manager/fuzz.rs#L111) on both Rust 1.67.0 and 1.67.1.
Users that uses our Docker images or binaries are unlikely affected, as our Docker images were built with `1.66`, and latest binaries were built with latest stable (`1.68.2`). It likely impacts user that builds from source using Rust versions 1.67.x.
## Proposed Changes
Bump Rust version (MSRV) to latest stable `1.68.2`.
## Additional Info
From `@Sea Monkey` on Lighthouse Discord:
> Crash on goerli using `unstable` `dd124b2d6804d02e4e221f29387a56775acccd08`
```
thread 'tokio-runtime-worker' panicked at 'Key must exist', /mnt/goerli/goerli/lighthouse/common/lru_cache/src/time.rs:68:28
stack backtrace:
Apr 15 09:37:36.993 WARN Peer sent invalid block in single block lookup, peer_id: 16Uiu2HAm6ZuyJpVpR6y51X4Enbp8EhRBqGycQsDMPX7e5XfPYznG, error: WouldRevertFinalizedSlot { block_slot: Slot(5420212), finalized_slot: Slot(5420224) }, root: 0x10f6…3165, service: sync
0: rust_begin_unwind
at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/std/src/panicking.rs:575:5
1: core::panicking::panic_fmt
at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/panicking.rs:64:14
2: core::panicking::panic_display
at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/panicking.rs:135:5
3: core::panicking::panic_str
at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/panicking.rs:119:5
4: core::option::expect_failed
at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/option.rs:1879:5
5: lru_cache::time::LRUTimeCache<Key>::raw_remove
6: lighthouse_network::peer_manager::PeerManager<TSpec>::handle_ban_operation
7: lighthouse_network::peer_manager::PeerManager<TSpec>::handle_score_action
8: lighthouse_network::peer_manager::PeerManager<TSpec>::report_peer
9: network::service::NetworkService<T>::spawn_service::{{closure}}
10: <futures_util::future::select::Select<A,B> as core::future::future::Future>::poll
11: <futures_util::future::future::map::Map<Fut,F> as core::future::future::Future>::poll
12: <futures_util::future::future::flatten::Flatten<Fut,<Fut as core::future::future::Future>::Output> as core::future::future::Future>::poll
13: tokio::loom::std::unsafe_cell::UnsafeCell<T>::with_mut
14: tokio::runtime::task::core::Core<T,S>::poll
15: tokio::runtime::task::harness::Harness<T,S>::poll
16: tokio::runtime::scheduler::multi_thread::worker::Context::run_task
17: tokio::runtime::scheduler::multi_thread::worker::Context::run
18: tokio::macros::scoped_tls::ScopedKey<T>::set
19: tokio::runtime::scheduler::multi_thread::worker::run
20: tokio::loom::std::unsafe_cell::UnsafeCell<T>::with_mut
21: tokio::runtime::task::core::Core<T,S>::poll
22: tokio::runtime::task::harness::Harness<T,S>::poll
23: tokio::runtime::blocking::pool::Inner::run
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
Apr 15 09:37:37.069 INFO Saved DHT state service: network
Apr 15 09:37:37.070 INFO Network service shutdown service: network
Apr 15 09:37:37.132 CRIT Task panic. This is a bug! advice: Please check above for a backtrace and notify the developers, message: <none>, task_name: network
Apr 15 09:37:37.132 INFO Internal shutdown received reason: Panic (fatal error)
Apr 15 09:37:37.133 INFO Shutting down.. reason: Failure("Panic (fatal error)")
Apr 15 09:37:37.135 WARN Unable to free worker error: channel closed, msg: did not free worker, shutdown may be underway
Apr 15 09:37:39.350 INFO Saved beacon chain to disk service: beacon
Panic (fatal error)
```
## Proposed Changes
* Bump Go from 1.17 to 1.20. The latest Geth release v1.11.0 requires 1.18 minimum.
* Prevent a cache miss during payload building by using the right fee recipient. This prevents Geth v1.11.0 from building a block with 0 transactions. The payload building mechanism is overhauled in the new Geth to improve the payload every 2s, and the tests were failing because we were falling back on a `getPayload` call with no lookahead due to `get_payload_id` cache miss caused by the mismatched fee recipient. Alternatively we could hack the tests to send `proposer_preparation_data`, but I think the static fee recipient is simpler for now.
* Add support for optionally enabling Lighthouse logs in the integration tests. Enable using `cargo run --release --features logging/test_logger`. This was very useful for debugging.
## Proposed Changes
Another `tree-states` motivated PR, this adds `jemalloc` as the default allocator, with an option to use the system allocator by compiling with `FEATURES="" make`.
- [x] Metrics
- [x] Test on Windows
- [x] Test on macOS
- [x] Test with `musl`
- [x] Metrics dashboard on `lighthouse-metrics` (https://github.com/sigp/lighthouse-metrics/pull/37)
Co-authored-by: Michael Sproul <micsproul@gmail.com>
I've needed to do this work in order to do some episub testing.
This version of libp2p has not yet been released, so this is left as a draft for when we wish to update.
Co-authored-by: Diva M <divma@protonmail.com>
## Issue Addressed
Closes#3709
## Proposed Changes
Add the job `compile-with-beta-compiler` to `test-suite`. This job has the following steps:
1. Use `actions/checkout@v3`. (Needed to run make in a later step.)
2. Install the dependencies listed in [build from source guide](https://lighthouse-book.sigmaprime.io/installation-source.html).
3. Change the compiler to the current beta version with `rustup override`.
4. Run `make`.
## Issue Addressed
Closes https://github.com/sigp/lighthouse/issues/3656
## Proposed Changes
* Replace `set-output` by `$GITHUB_OUTPUT` usage
* Avoid rate-limits when installing `protoc` by making authenticated requests (continuation of https://github.com/sigp/lighthouse/pull/3621)
* Upgrade all Ubuntu 18.04 usage to 22.04 (18.04 is end of life)
* Upgrade macOS-latest to explicit macOS-12 to silence warning
* Use `actions/checkout@v3` and `actions/cache@v3` to avoid deprecated NodeJS v12
## Additional Info
Can't silence the NodeJS warnings entirely due to https://github.com/sigp/lighthouse/issues/3705. Can fix that in future.
## Issue Addressed
NA
## Proposed Changes
Bump versions to v3.0.0
## Additional Info
- ~~Blocked on #3439~~
- ~~Blocked on #3459~~
- ~~Blocked on #3463~~
- ~~Blocked on #3462~~
- ~~Requires further testing~~
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
## Proposed Changes
Enable multiple database backends for the slasher, either MDBX (default) or LMDB. The backend can be selected using `--slasher-backend={lmdb,mdbx}`.
## Additional Info
In order to abstract over the two library's different handling of database lifetimes I've used `Box::leak` to give the `Environment` type a `'static` lifetime. This was the only way I could think of using 100% safe code to construct a self-referential struct `SlasherDB`, where the `OpenDatabases` refers to the `Environment`. I think this is OK, as the `Environment` is expected to live for the life of the program, and both database engines leave the database in a consistent state after each write. The memory claimed for memory-mapping will be freed by the OS and appropriately flushed regardless of whether the `Environment` is actually dropped.
We are depending on two `sigp` forks of `libmdbx-rs` and `lmdb-rs`, to give us greater control over MDBX OS support and LMDB's version.
## Issue Addressed
Which issue # does this PR address?
## Proposed Changes
Please list or describe the changes introduced by this PR.
## Additional Info
Please provide any additional information. For example, future considerations
or information useful for reviewers.
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Issue Addressed
N/A
## Proposed Changes
Make simulator merge compatible. Adds a `--post_merge` flag to the eth1 simulator that enables a ttd and simulates the merge transition. Uses the `MockServer` in the execution layer test utils to simulate a dummy execution node.
Adds the merge transition simulation to CI.
## Description
Add a new lint to CI that attempts to detect calls to functions like `block_on` from async execution contexts. This lint was written from scratch exactly for this purpose, on my fork of Clippy: https://github.com/michaelsproul/rust-clippy/tree/disallow-from-async
## Additional Info
- I've successfully detected the previous two issues we had with `block_on` by running the linter on the commits prior to each of these PRs: https://github.com/sigp/lighthouse/pull/3165, https://github.com/sigp/lighthouse/pull/3199.
- The lint runs on CI with `continue-on-error: true` so that if it fails spuriously it won't block CI.
- I think it would be good to merge this PR before https://github.com/sigp/lighthouse/pull/3244 so that we can lint the extensive executor-related changes in that PR.
- I aim to upstream the lint to Clippy, at which point building a custom version of Clippy from my fork will no longer be necessary. I imagine this will take several weeks or months though, because the code is currently a bit hacky and will need some renovations to pass review.
## Issue Addressed
This fixes the low-hanging Clippy lints introduced in Rust 1.61 (due any hour now). It _ignores_ one lint, because fixing it requires a structural refactor of the validator client that needs to be done delicately. I've started on that refactor and will create another PR that can be reviewed in more depth in the coming days. I think we should merge this PR in the meantime to unblock CI.
## Issue Addressed
Attempt to fix CI
## Proposed Changes
- ~~install `node-gyp-build` which should look for prebuilt binaries for `@truffle-suite/bigint_buffer`. This should make it so we don't have to build it directly. See: https://github.com/trufflesuite/ganache/pull/1414~~ this didn't work
- This also uses the `setup-node` action because it includes caching. Sort of a shot in the dark, but the ganache github repo uses it and the failures seem to be for missing files in a node cache
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Issue Addressed
Hopefully makes windows ganache installation more reliable.
## Proposed Changes
- use `chocolatey` to install windows build tools. This seems to often be the prescribed solution for `node gyp` issues. `chocolatey` is used here because `npm install --global --production windows-build-tools` hangs in github actions
## Additional Info
I still haven't found why the prior installation technique would sometimes work, the `windows-2019` environments seem to be identical across successes and failures. I think this should be re-run a few times to see if it can consistently pass
Co-authored-by: realbigsean <sean@sigmaprime.io>
## Proposed Changes
Set a minimum supported Rust version (MSRV) in the `Cargo.toml` for the Lighthouse binary so that attempts to compile it with an outdated compiler fail immediately with a clear error.
To ensure that the codebase builds with the MSRV I've also added a Github actions job that runs `cargo check` using the MSRV extracted from `Cargo.toml`. This will force us to keep it up to date.
I opted to use `cargo check` rather than Clippy because Clippy frequently introduces new lints that we adopt, so our MSRV for Clippy is usually the most recent Rust version, while the MSRV for building Lighthouse is older.
## Issue Addressed
As discussed on last-night's consensus call, the testnets next week will target the [Kiln Spec v2](https://hackmd.io/@n0ble/kiln-spec).
Presently, we support Kiln V1. V2 is backwards compatible, except for renaming `random` to `prev_randao` in:
- https://github.com/ethereum/execution-apis/pull/180
- https://github.com/ethereum/consensus-specs/pull/2835
With this PR we'll no longer be compatible with the existing Kintsugi and Kiln testnets, however we'll be ready for the testnets next week. I raised this breaking change in the call last night, we are all keen to move forward and break things.
We now target the [`merge-kiln-v2`](https://github.com/MariusVanDerWijden/go-ethereum/tree/merge-kiln-v2) branch for interop with Geth. This required adding the `--http.aauthport` to the tester to avoid a port conflict at startup.
### Changes to exec integration tests
There's some change in the `merge-kiln-v2` version of Geth that means it can't compile on a vanilla Github runner. Bumping the `go` version on the runner solved this issue.
Whilst addressing this, I refactored the `testing/execution_integration` crate to be a *binary* rather than a *library* with tests. This means that we don't need to run the `build.rs` and build Geth whenever someone runs `make lint` or `make test-release`. This is nice for everyday users, but it's also nice for CI so that we can have a specific runner for these tests and we don't need to ensure *all* runners support everything required to build all execution clients.
## More Info
- [x] ~~EF tests are failing since the rename has broken some tests that reference the old field name. I have been told there will be new tests released in the coming days (25/02/22 or 26/02/22).~~
## Issue Addressed
Timeouts due to Windows builds running for 2h 20m.
## Proposed Changes
* Increase Bors timeout to 3h
* Refine the target branch check so that it will pass when we make PRs to feature branches. This is just an extra change I've been meaning to sneak in for a while.
## Additional Info
* I think it would also be cool to try caching for CI again, but that's a separate issue and we'll still need the long timeout on a cache miss.
## Issue Addressed
NA
## Proposed Changes
This PR extends #3018 to address my review comments there and add automated integration tests with Geth (and other implementations, in the future).
I've also de-duplicated the "unused port" logic by creating an `common/unused_port` crate.
## Additional Info
I'm not sure if we want to merge this PR, or update #3018 and merge that. I don't mind, I'm primarily opening this PR to make sure CI works.
Co-authored-by: Mark Mackey <mark@sigmaprime.io>
## Issue Addressed
Closes#2938
## Proposed Changes
* Build and publish images with a `-modern` suffix which enable CPU optimizations for modern hardware.
* Add docs for the plethora of available images!
* Unify all the Docker workflows in `docker.yml` (including for tagged releases).
## Additional Info
The `Dockerfile` is no longer used by our Docker Hub builds, as we use `cross` and a generic approach for ARM and x86. There's a new CI job `docker-build-from-source` which tests the `Dockerfile` without publishing anything.
## Issue Addressed
Closes#2286Closes#2538Closes#2342
## Proposed Changes
Part II of major slasher optimisations after #2767
These changes will be backwards-incompatible due to the move to MDBX (and the schema change) 😱
* [x] Shrink attester keys from 16 bytes to 7 bytes.
* [x] Shrink attester records from 64 bytes to 6 bytes.
* [x] Separate `DiskConfig` from regular `Config`.
* [x] Add configuration for the LRU cache size.
* [x] Add a "migration" that deletes any legacy LMDB database.
## Issue Addressed
This is related to #1926 and #1712.
## Proposed Changes
This PR adds a test that make sure that the used dependencies can be vendored.
Being able to vendor the dependencies is important for archival and repdroducibility purpose.
It's also required to package lighthouse for some Linux distributions. Specifically [NixOS](https://nixos.org/) and [Yocto](https://www.yoctoproject.org/).
## Additional Info
This PR only adds the test, it doesn't clean up the dependencies yet. That's why it is in draft.
## Issue Addressed
NA
## Proposed Changes
Adds some more testing for Altair to the op pool. Credits to @michaelsproul for some appropriated efforts here.
## Additional Info
NA
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
## Issue Addressed
Resolves#2069
## Proposed Changes
- Adds a `--doppelganger-detection` flag
- Adds a `lighthouse/seen_validators` endpoint, which will make it so the lighthouse VC is not interopable with other client beacon nodes if the `--doppelganger-detection` flag is used, but hopefully this will become standardized. Relevant Eth2 API repo issue: https://github.com/ethereum/eth2.0-APIs/issues/64
- If the `--doppelganger-detection` flag is used, the VC will wait until the beacon node is synced, and then wait an additional 2 epochs. The reason for this is to make sure the beacon node is able to subscribe to the subnets our validators should be attesting on. I think an alternative would be to have the beacon node subscribe to all subnets for 2+ epochs on startup by default.
## Additional Info
I'd like to add tests and would appreciate feedback.
TODO: handle validators started via the API, potentially make this default behavior
Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
## Proposed Changes
Implement the consensus changes necessary for the upcoming Altair hard fork.
## Additional Info
This is quite a heavy refactor, with pivotal types like the `BeaconState` and `BeaconBlock` changing from structs to enums. This ripples through the whole codebase with field accesses changing to methods, e.g. `state.slot` => `state.slot()`.
Co-authored-by: realbigsean <seananderson33@gmail.com>
## Issue Addressed
`make lint` failing on rust 1.53.0.
## Proposed Changes
1.53.0 updates
## Additional Info
I haven't figure out why yet, we were now hitting the recursion limit in a few crates. So I had to add `#![recursion_limit = "256"]` in a few places
Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
## Issue Addressed
Windows incompatibility.
## Proposed Changes
On windows, lighthouse needs to default to STDIN as tty doesn't exist. Also Windows uses ACLs for file permissions. So to mirror chmod 600, we will remove every entry in a file's ACL and add only a single SID that is an alias for the file owner.
Beyond that, there were several changes made to different unit tests because windows has slightly different error messages as well as frustrating nuances around killing a process :/
## Additional Info
Tested on my Windows VM and it appears to work, also compiled & tested on Linux with these changes. Permissions look correct on both platforms now. Just waiting for my validator to activate on Prater so I can test running full validator client on windows.
Co-authored-by: ethDreamer <37123614+ethDreamer@users.noreply.github.com>
Co-authored-by: Michael Sproul <micsproul@gmail.com>
## Issue Addressed
NA
## Proposed Changes
Rust 1.50 has landed 🎉
The shiny new `clippy` peers down upon us mere mortals with disgust. Brutish peasants wrapping our `usize`s in superfluous `Option`s... tsk tsk.
I've performed the goat sacrifice and corrected our evil ways in this PR. Tonight we shall pray that Github Actions bestows the almighty green tick upon us.
## Additional Info
NA
Co-authored-by: realbigsean <seananderson33@gmail.com>
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
Attempt to prevent accidental merges to `stable` due to GitHub's default behaviour of opening PRs against it.
I've intentionally opened this PR against `stable` to test the functionality ;)
## Issue Addressed
N/A
## Proposed Changes
I didn't realize the `PORTABLE` env variable is only picked up by `install` in the `Makefile` so we are still getting `SIGILL`s:
https://github.com/sigp/lighthouse/runs/1565004525?check_suite_focus=true
## Additional Info
Co-authored-by: realbigsean <seananderson33@gmail.com>
## Issue Addressed
NA
## Proposed Changes
Fixes problems with slot times below 1 second which got revealed by running the syncing simulator with the default speedup time.
## Issue Addressed
N/A
## Proposed Changes
Add some caching to the test suite and to the aarch64 cross-compile in the docker build.
## Additional Info
Cache hits only occur if the Cargo.lock file is unchanged, Github Actions runner OS matches, and the cache is "in scope". Some documentation on github actions cache scoping is here:
https://docs.github.com/en/free-pro-team@latest/actions/guides/caching-dependencies-to-speed-up-workflows#matching-a-cache-key
I'm not sure how frequently we'll get cache hits, I imagine only on smaller PR's or updates to the same PR. And there is a cache size limit that we may end up reaching quickly. But Github actions handles evictions if we go over that limit.
Not sure how much of an impact this will end up having but I don't really see a downside to trying it out.
Co-authored-by: realbigsean <seananderson33@gmail.com>
## Issue Addressed
N/A
## Proposed Changes
Remove the MacOs tests. They routinely fail, causing bors to retry and slowing down the whole merge process.
## Additional Info
N/A
Co-authored-by: Michael Sproul <michael@sigmaprime.io>
## Issue Addressed
Resolves#1100
## Proposed Changes
* Implement the `SafeArith` trait for `Slot` and `Epoch`, so that methods like `safe_add` become available.
* Tweak the `SafeArith` trait to allow a different `Rhs` type (analagous to `std::ops::Add`, etc).
* Add a `legacy-arith` feature to `types` and `state_processing` that conditionally enables implementations of
the `std` ops with saturating semantics.
* Check compilation of `types` and `state_processing` _without_ `legacy-arith` on CI,
thus guaranteeing that they only use the `SafeArith` primitives 🎉
## Additional Info
The `legacy-arith` feature gets turned on by all higher-level crates that depend on `state_processing` or `types`, thus allowing the beacon chain, networking, and other components to continue to rely on the availability of ops like `+`, `-`, `*`, etc.
**This is a consensus-breaking change**, but brings us in line with the spec, and our incompatibilities shouldn't have been reachable with any valid configuration of Eth2 parameters.
