Tidy app gas accounting loop and tests

[masih]

• Remove nonzeroTxsCnt: declared and incremented but never read.
• Remove a stale "Skipping" inline comment that no longer describes
  the branch it sits next to.
• Reduce allocations and optimise for fast path on decode failure.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	May 22, 2026, 7:54 AM

[codecov]

Codecov Report

❌ Patch coverage is 83.72093% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.09%. Comparing base (d4fc9c5) to head (c7c0ad3).

Files with missing lines	Patch %	Lines
app/app.go	83.72%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3464      +/-   ##
==========================================
- Coverage   59.11%   59.09%   -0.03%     
==========================================
  Files        2187     2187              
  Lines      182237   182039     -198     
==========================================
- Hits       107730   107570     -160     
+ Misses      64851    64821      -30     
+ Partials     9656     9648       -8     

Flag	Coverage Δ
sei-chain-pr	50.46% <83.72%> (?)
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
app/app.go	68.80% <83.72%> (-0.60%)	⬇️

... and 39 files with indirect coverage changes

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[cursor]

PR Summary

High Risk
Touches consensus-critical proposal processing and block gas limit checks; behavior changes (fail-fast on decode errors/nil txs and stricter error propagation) could cause unexpected proposal rejections if edge cases differ from prior handling.

Overview
Tightens proposal-time transaction decoding and block gas validation. ProcessProposalHandler now decodes tx bytes via a context-aware DecodeTxBytesConcurrently that uses errgroup with a worker limit, fails fast on decode errors/panics, and rejects the proposal immediately when decoding fails.

Refactors checkTotalBlockGas semantics and safety. The gas accounting loop is simplified (removes unused counters, adds explicit overflow guards, consolidates max-gas checks) and now treats any nil decoded tx as an immediate rejection instead of skipping it; logic around gasless heuristics and EVM gas-estimate vs gas-wanted selection is clarified.

Updates and expands tests. The checkTotalBlockGas tests are refactored with shared helpers, updated to assert the new nil-tx rejection behavior, and add coverage for preferring valid EVM gas estimates over gasWanted.

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[cursor]

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