chore(tests-benchmark, ci): mark test_keccak_max_permutations as slow

[danceratopz]

🗒️ Description

test_keccak_max_permutations is by far the most expensive test in the bench-gas smoke check: It fills in ~465s per format, while the next slowest benchmark fills in ~12s. The test searches for the input size that maximizes keccak permutations per block and then fills a maximal block, and that work is repeated per fixture format.

Marking it @pytest.mark.slow excludes it from the smoke check (just bench-gas and the benchmark sanity checks run -m "not slow"), consistent with the existing slow benchmarks test_blockhash and test_bls12_g2_msm. The release benchmark matrix (.github/configs/feature.yaml) does not filter slow, so the test still ships in the released fixtures.

🔗 Related Issues or PRs

Addresses #2673. Complements #3057 (fill only the blockchain_test format in bench-gas): Even with that format reduction the test still fills once at ~465s and sets the smoke check's floor, and this marker removes it.

✅ Checklist

• All: Ran fast static checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  just static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.22%. Comparing base (3f888bc) to head (93dd354).

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #3058   +/-   ##
================================================
  Coverage            93.22%   93.22%           
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  Files                  624      624           
  Lines                36926    36926           
  Branches              3377     3377           
================================================
  Hits                 34424    34424           
  Misses                1708     1708           
  Partials               794      794           

Flag	Coverage Δ
unittests	93.22% <ø> (ø)

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[danceratopz]

This shouldn't be required with:

• refactor(test-benchmark): speed-up the keccak max-permutations search #3060