*: take care of anti-MEV part

[AnnaShaleva]

1. For anti-MEV extension it's possible that some commits carry invalid share which is impossible to check at the commit verification level. In this case node should collect some more commits. Hence, ProcessBlock callback signature is extended with error return value. The general idea is similar to PreBlock processing behaviour.
2. Remove PreCommit with invalid signature from cache.
3. Log Commit signature verification error.
4. Add VerifyCommit callback.

[codecov]

Codecov Report

Attention: Patch coverage is 32.14286% with 19 lines in your changes missing coverage. Please review.

Project coverage is 58.24%. Comparing base (94bc382) to head (be64b5f).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
check.go	27.27%	7 Missing and 1 partial ⚠️
dbft.go	12.50%	6 Missing and 1 partial ⚠️
config.go	71.42%	2 Missing ⚠️
internal/simulation/main.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #134      +/-   ##
==========================================
- Coverage   58.61%   58.24%   -0.37%     
==========================================
  Files          32       32              
  Lines        2235     2256      +21     
==========================================
+ Hits         1310     1314       +4     
- Misses        843      858      +15     
- Partials       82       84       +2     

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[AnnaShaleva]

@roman-khimov, review please, but simulation/CHANGELOG check are failing; will check what's happened with simulation.

[AnnaShaleva]

Simulation is fixed by #135; CHANGELOG is updated.