fix(consensus): prevent double signing after a crash or restart

[oXtxNt9U]

Summary

• Validators now durably record the last signed position (blockNumber/round/step + value)
• After a restart signing a conflicting message at or below the recorded position throws DoubleSignError instead
• The proposal/prevote/precommit is skipped with a warning and the validator resumes at the next round/height on its own

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.76%. Comparing base (87365ff) to head (e234065).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1449      +/-   ##
===========================================
+ Coverage    77.34%   77.76%   +0.41%     
===========================================
  Files          922      934      +12     
  Lines        15954    16415     +461     
  Branches      2167     2260      +93     
===========================================
+ Hits         12340    12765     +425     
- Misses        3609     3643      +34     
- Partials         5        7       +2     

Flag	Coverage Δ
contracts	91.76% <ø> (?)
packages	77.38% <100.00%> (+0.03%)	⬆️

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