bug(test-benchmark): update code padding in fixed opcode count mode

[LouisTsai-Csie]

🗒️ Description

Summary

• Fix benchmark tests hitting INVALID opcode when using --fixed-opcode-count
• Add STOP instruction before padding in generate_repeated_code to ensure clean termination

Problem

• When fixed_opcode_count is set, the generated code was:
• setup + JUMPDEST + attack_block * N + INVALID padding

After executing all iterations, execution fell through into INVALID padding.

Solution

• Insert STOP before padding:
• setup + JUMPDEST + attack_block * N + STOP + INVALID padding

🔗 Related Issues or PRs

N/A.

✅ Checklist

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

  uvx tox -e 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 adding an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.
• Tests: For PRs implementing a missed test case, update the post-mortem document to add an entry the list.
• Ported Tests: All converted JSON/YML tests from ethereum/tests or tests/static have been assigned @ported_from marker.

Cute Animal Picture

[spencer-tb]

LGTM!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.33%. Comparing base (685eba7) to head (b76e4b8).
⚠️ Report is 4 commits behind head on forks/amsterdam.

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #1983   +/-   ##
================================================
  Coverage            86.33%   86.33%           
================================================
  Files                  538      538           
  Lines                34557    34557           
  Branches              3222     3222           
================================================
  Hits                 29835    29835           
  Misses                4148     4148           
  Partials               574      574           

Flag	Coverage Δ
unittests	86.33% <ø> (ø)

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