Migrate Equivocation Handling to x/evidence

[alexanderbez]

• Move HandleDoubleSign from x/slashing to the x/evidence module
• Move double sign params from x/slashing to the x/evidence module
• Cleanup specs
• Add params handler to x/evidence client logic

closes: #5296

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• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

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[codecov]

Codecov Report

Merging #5299 into master will decrease coverage by <.01%.
The diff coverage is 67.9%.

@@            Coverage Diff             @@
##           master    #5299      +/-   ##
==========================================
- Coverage   54.79%   54.79%   -0.01%     
==========================================
  Files         307      311       +4     
  Lines       18296    18386      +90     
==========================================
+ Hits        10026    10075      +49     
- Misses       7494     7540      +46     
+ Partials      776      771       -5

[fedekunze]

Thanks @alexanderbez for doing this refactor. The distinctions between modules are much clearer now 👏

I left some questions but otherwise LGTM

[fedekunze]

q: shouldn't every evidence type define its own evidence age instead?

[alexanderbez]

I don't think so because all evidence must be within the unbonding period. Perhaps certain evidence can have even smaller valid periods (e.g. 1/2 unbonding period), but I don't see any immediate use-cases or evidence types that need this.

[AdityaSripal]

Great work! Small nitpicks

Only important question is why DoubleSignJailTime is treated as a constant rather than as a parameter

[AdityaSripal]

Also a heads-up, the Evidence interface got changed in #5321 to accomodate chain misbehaviour. Might require some changes to this PR but nothing substantial.

Would just require asserting that the Equivocation struct satified ValidatorEvidence interface rather than looser Evidence interface

[alexanderbez]

@AdityaSripal @fedekunze I've updated and addressed all comments.

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Also a heads-up, the Evidence interface got changed in #5321 to accomodate chain misbehaviour. Might require some changes to this PR but nothing substantial.

Would just require asserting that the Equivocation struct satified ValidatorEvidence interface rather than looser Evidence interface

How so? What if we merge this PR first? I haven't looked at the PR yet, but I imagine the stricter interface contract is warranted?

[AdityaSripal]

The new ValidatorEvidence interface is identical to the current Evidence interface.

The original Evidence interface was made looser in #5321 to accommodate other forms of Evidence that are not Validator-specific; namely entire chains misbehaving

We can merge this PR first, would require a trivial change to fix things once my PR is merged so i can do that.

[alexanderbez]

Great! Sounds like a plan. Thanks for the review <3