fix(test-logging): don't store empty logs

[felix314159]

🗒️ Description

Before this PR, when u run e.g. uv run fill --pytest-help it will create an empty log file. I have noticed empty log files in the past and this is just a minimal example to demonstrate it.

The PR fixes it so that no completely empty log files are created. Writing non-empty logs still works, e.g. run uv run fill -v -s --no-html --clean 'tests/frontier/touch/test_touch.py::test_zero_gas_price_and_touching[fork_Frontier-state_test]' after applying the PR.

🔗 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 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.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.35%. Comparing base (878ef15) to head (0000000).
⚠️ Report is 5 commits behind head on forks/amsterdam.

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #2547   +/-   ##
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  Coverage            86.35%   86.35%           
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  Files                  599      599           
  Lines                36904    36904           
  Branches              3771     3771           
================================================
  Hits                 31868    31868           
  Misses                4485     4485           
  Partials               551      551           

Flag	Coverage Δ
unittests	86.35% <ø> (ø)

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[danceratopz]

Thanks @felix314159. TIL delay=True!