feat: mempool: return all EVM txs before others when reaping

[arajasek]

Describe your changes and provide context

As a result, validators using this mempool logic will produce blocks with a batch of EVM txs, followed by any non-EVM txs. This will allow us to use future executors that can only run EVM txs to run a bigger batch of EVM txs, falling back to existing executors for all non-EVM and interop behaviour.

Note that:

• this PR is NOT consensus-breaking. this is only a mempool operation, not a change to the rules of the protocol.
• this PR does NOT change which txs the mempool reaps. the exact same txs are selected as before, just ordered to be a contiguous slab of EVM txs, followed by a slab of non-EVM ones.

Testing performed to validate your change

Added a new test, all tests pass

[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	Jan 8, 2026, 2:39 PM

[arajasek]

Note the ReapMaxTxs method's behaviour is not changed by this PR, since that method is used for RPC etc. support (and not for block creation).

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 43.82%. Comparing base (4107264) to head (b791d79).

Files with missing lines	Patch %	Lines
sei-tendermint/internal/mempool/mempool.go	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2669      +/-   ##
==========================================
+ Coverage   43.79%   43.82%   +0.02%     
==========================================
  Files        1908     1908              
  Lines      159047   159053       +6     
==========================================
+ Hits        69659    69706      +47     
+ Misses      82981    82939      -42     
- Partials     6407     6408       +1     

Flag	Coverage Δ
sei-chain	45.89% <ø> (ø)
sei-cosmos	38.20% <ø> (ø)
sei-db	69.13% <ø> (ø)
sei-tendermint	47.33% <91.66%> (+0.13%)	⬆️

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Files with missing lines	Coverage Δ
sei-tendermint/internal/mempool/mempool.go	68.11% <91.66%> (+0.33%)	⬆️

... and 18 files with indirect coverage changes

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