Move slashing protection failure metric out of ValidatorDB

[syjn99]

What type of PR is this?

Other

What does this PR do? Why is it needed?

Introduced in:

• Implement EIP-3076 minimal slashing protection, using a filesystem database #13360

SlashableAttestationCheck and SlashableProposalCheck both have two arguments: a metric (ValidatorAttestFailVec, ValidatorProposeFailVec) and a flag (v.emitAccountMetrics). Validator*FailVec is incremented conditionally (and bit inconsistently) inside those methods.

This PR completely moves failure metrics out of ValidatorDB, and handles them consistently, after each call. This PR also removes double counting problem for ValidatorProposeFailVec: It can be first incremented in SlashableProposalCheck and then incremented again at the caller side.

• Implement EIP-3076 minimal slashing protection, using a filesystem database #13360 (comment)

I guess it was a mechnical change in order to preserve the same semantics regarding metrics, but as 1) we already have the double counting issue in proposal metrics 2) for sake of consistency and 3) it should be considered as "failure" when slashing protection check fails, I'd suggest to handle like this PR.

Which issue(s) does this PR fix?

N/A

Other notes for review

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).