fix to ProposalPOLMessage poisoning (CON-222)

[pompon0]

The bug was about panic after setting vote at out of range index. Added a test. Additionally I have also made getters return bool to indicate if get succeeded.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Mar 27, 2026, 5:01 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.74%. Comparing base (82751c6) to head (a101810).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3129      +/-   ##
==========================================
- Coverage   58.75%   58.74%   -0.01%     
==========================================
  Files        2094     2094              
  Lines      173084   173009      -75     
==========================================
- Hits       101696   101637      -59     
+ Misses      62333    62323      -10     
+ Partials     9055     9049       -6     

Flag	Coverage Δ
sei-db	70.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-tendermint/internal/consensus/msgs.go	81.60% <ø> (ø)
sei-tendermint/internal/consensus/peer_state.go	84.10% <ø> (-0.39%)	⬇️
sei-tendermint/internal/consensus/reactor.go	68.84% <ø> (+0.06%)	⬆️
sei-tendermint/internal/consensus/state.go	74.31% <ø> (+0.01%)	⬆️
...rmint/internal/consensus/types/peer_round_state.go	100.00% <ø> (ø)
...tendermint/internal/consensus/types/round_state.go	86.36% <ø> (-0.10%)	⬇️
sei-tendermint/internal/evidence/verify.go	74.82% <ø> (+0.17%)	⬆️
sei-tendermint/internal/rpc/core/status.go	80.51% <ø> (-0.50%)	⬇️
sei-tendermint/node/setup.go	67.29% <ø> (+0.25%)	⬆️
sei-tendermint/test/e2e/runner/evidence.go	0.00% <ø> (ø)
... and 7 more

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