fix(consensus): correct locked and valid value handling across rounds and restarts

[oXtxNt9U]

Summary

• onProposal prevoted any valid proposal regardless of the lock, so a validator locked on one block could help a conflicting one reach +2/3 in a later round
• #signProposal re-proposed a restored valid value without deserializing its payload, throwing into an unawaited promise and killing the node on startup
• onProposalLocked prevoted nil for a lock-proven proposal whenever the proposer's validRound predated the lock even when the proposal was for the very block the validator was locked on, wasting a round each time

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 77.96%. Comparing base (58176af) to head (1bb461e).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1450      +/-   ##
===========================================
+ Coverage    77.57%   77.96%   +0.39%     
===========================================
  Files          923      934      +11     
  Lines        16019    16463     +444     
  Branches      2205     2286      +81     
===========================================
+ Hits         12426    12835     +409     
- Misses        3588     3621      +33     
- Partials         5        7       +2     

Flag	Coverage Δ
contracts	91.76% <ø> (?)
packages	77.58% <100.00%> (+0.01%)	⬆️

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