## 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
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
