## 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
Replaces #2091
## Proposed Changes
* Delete the uncompressed genesis states from `eth2_network_config` after they were merged accidentally in #2029.
* Tweak the build script to not overwrite `genesis.ssz` on every build, which caused spurious rebuilds.
## Issue Addressed
Implements support for importing and exporting the slashing protection DB interchange format described here:
https://hackmd.io/@sproul/Bk0Y0qdGD
Also closes#1584
## Proposed Changes
* [x] Support for serializing and deserializing the format
* [x] Support for importing and exporting Lighthouse's database
* [x] CLI commands to invoke import and export
* [x] Export to minimal format (required when a minimal format has been previously imported)
* [x] Tests for export to minimal (utilising mixed importing and attestation signing?)
* [x] Tests for import/export of complete format, and import of minimal format
* [x] ~~Prevent attestations with sources less than our max source (Danny's suggestion). Required for the fake attestation that we put in for the minimal format to block attestations from source 0.~~
* [x] Add the concept of a "low watermark" for compatibility with the minimal format
Bonus!
* [x] A fix to a potentially nasty bug involving validators getting re-registered each time the validator client ran! Thankfully, the ordering of keys meant that the validator IDs used for attestations and blocks remained stable -- otherwise we could have had some slashings on our hands! 😱
* [x] Tests to confirm that this bug is indeed vanquished
## Issue Addressed
NA
## Proposed Changes
This PR commits the `Cargo.lock` file so it does not indicate a dirty git tree in the version tag. This code should be used for the `v0.2.3` release.
Also, adds a `Makefile` command to produce tarballs for upload on release.
## Additional Info
NA
