feat: mempool: don't add pending txs to priority reservoir

[arajasek]

We don't know whether pending txs will actually ever land, so they can throw off our metrics for utilization and priority reservoir.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jan 5, 2026, 3:26 PM

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 43.79%. Comparing base (354a415) to head (2f6c13d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sei-tendermint/internal/mempool/mempool.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2641      +/-   ##
==========================================
- Coverage   46.38%   43.79%   -2.60%     
==========================================
  Files        1237     1904     +667     
  Lines      108362   158932   +50570     
==========================================
+ Hits        50265    69604   +19339     
- Misses      53489    82931   +29442     
- Partials     4608     6397    +1789     

Flag	Coverage Δ
sei-chain	45.83% <ø> (+0.02%)	⬆️
sei-cosmos	38.20% <ø> (?)
sei-db	69.28% <ø> (+0.21%)	⬆️
sei-tendermint	47.31% <50.00%> (-0.02%)	⬇️

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Files with missing lines	Coverage Δ
sei-tendermint/internal/mempool/mempool.go	67.78% <50.00%> (ø)

... and 687 files with indirect coverage changes

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[masih]

Nice work, thanks @arajasek 🍻