## Issue Addressed
Closes#2354
## Proposed Changes
Add a `minify` method to `slashing_protection::Interchange` that keeps only the maximum-epoch attestation and maximum-slot block for each validator. Specifically, `minify` constructs "synthetic" attestations (with no `signing_root`) containing the maximum source epoch _and_ the maximum target epoch from the input. This is equivalent to the `minify_synth` algorithm that I've formally verified in this repository:
https://github.com/michaelsproul/slashing-proofs
## Additional Info
Includes the JSON loading optimisation from #2347
## Issue Addressed
Closes#1873
## Proposed Changes
Fixes the bug in slashing protection import (#1873) by pruning the database upon import.
Also expands the test generator to cover this case and a few others which are under discussion here:
https://ethereum-magicians.org/t/eip-3076-validator-client-interchange-format-slashing-protection/4883
## Additional Info
Depending on the outcome of the discussion on Eth Magicians, we can either wait for consensus before merging, or merge our preferred solution and patch things later.
## Issue Addressed
NA
## Proposed Changes
Updates the validator guide to provide instructions for mainnet users.
## Additional Info
- ~~Blocked on #1751~~
## Proposed Changes
Update the slashing protection interchange format to v5 in preparation for finalisation as part of an EIP.
Also, add some more tests and update the commit hash for https://github.com/eth2-clients/slashing-protection-interchange-tests to include the new generated tests.
## Proposed Changes
* Add documentation about slashing protection, including how to troubleshoot issues and move between clients.
* Add an error message if the validator client is started with 0 validators. Previously it would hit an error relating to the slashing protection database not existing, which wrongly pushed people towards using the unsafe `--init-slashing-protection` flag.
