fix(test-tests): Add fork name to cached blob filename to prevent xdist flakes

[kclowes]

🗒️ Description

I ran into a race condition in test-tests-pypy this morning where the test calls Blob.from_fork for two parametrized cases running in parallel — CancunToPragueAtTime15k at ts=14999 (resolves to Cancun) and at ts=15000 (resolves to Prague). Both resolve to read from blob_0_cell_proofs_0.json under the old naming.

If the Cancun worker ran first and wrote the file with "fork": "Cancun" stored in the JSON, the Prague worker would find the file already exists, load it, and get back a blob with fork=Cancun. The test then asserts b.fork.name() ==
"Prague" and fails.

🔗 Related Issues or PRs

N/A.

✅ 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).
• 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 90.43%. Comparing base (1787c74) to head (d00c68e).
⚠️ Report is 1 commits behind head on forks/amsterdam.

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #2930   +/-   ##
================================================
  Coverage            90.43%   90.43%           
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  Files                  535      535           
  Lines                32430    32430           
  Branches              3012     3012           
================================================
  Hits                 29329    29329           
  Misses                2573     2573           
  Partials               528      528           

Flag	Coverage Δ
unittests	90.43% <ø> (ø)

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