fix: mempool: enforce txBlacklisting for stupidly big txs

[arajasek]

Describe your changes and provide context

This PR:

• changes mempool config to have CheckTxErrorBlacklistEnabled true by default
• weakens blacklist protection to apply to only oversized transactions.

Future PRs will expand blacklist protection to cover other forms of "clearly bad" transactions, such as:

• undecodeable transactions
• incorrect signatures
• ludicrous params (more gas than a block has)
• etc.

Testing performed to validate your change

make test passes

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 16, 2025, 5:45 PM

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 43.22%. Comparing base (2f2a636) to head (ece4ece).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sei-tendermint/internal/mempool/mempool.go	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2590      +/-   ##
==========================================
- Coverage   43.22%   43.22%   -0.01%     
==========================================
  Files        1857     1857              
  Lines      153120   153124       +4     
==========================================
- Hits        66184    66182       -2     
- Misses      81020    81022       +2     
- Partials     5916     5920       +4     

Flag	Coverage Δ
sei-chain	41.93% <ø> (-0.01%)	⬇️
sei-cosmos	38.03% <ø> (+<0.01%)	⬆️
sei-db	69.06% <ø> (ø)
sei-ibc-go	55.96% <ø> (ø)
sei-tendermint	47.50% <90.00%> (-0.02%)	⬇️
sei-wasmd	42.18% <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/mempool/mempool.go	67.78% <90.00%> (+0.05%)	⬆️

... and 17 files with indirect coverage changes

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