feat(pytest): use node id as fixture name

[danceratopz]

🗒️ Description

This PR:

• Changes the test fixture names (the keys in the top-level dict used in JSON fixture files) to use the corresponding pytest node id.
• Replaces "=" with "_", although this slightly impacts readability, this will reduce friction along the tool chain. Rationale here:
  • feat(fw): use pytest nodeids as test names in json fixtures #329 (comment) (dotnet),
  • feat(fw): use pytest nodeids as test names in json fixtures #329 (comment) (pytest).

🔗 Related Issues

Fixes #329.

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• Tests: Included the type and version of evm t8n tool used to locally execute test cases: e.g., ref with commit hash or geth 1.13.1-stable-3f40e65.
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.

[marioevz]

LGTM! Thanks :)

[spencer-tb]

LGTM - I like it a lot!

Maybe we could rename test_filler.py to:

• pytest_filler.py
• plugin_filler.py

Then for src/ethereum_test_tools/tests/test_filler.py, we could rename this to framework_filler.py.

Then again test_test_filler.py makes me smile :)

[danceratopz]

LGTM - I like it a lot!

Maybe we could rename test_filler.py to:

* `pytest_filler.py`

* `plugin_filler.py`

Then for src/ethereum_test_tools/tests/test_filler.py, we could rename this to framework_filler.py.

Then again test_test_filler.py makes me smile :)

Hehe, as mentioned offline, one possibility is renaming test_filler to fixture_filler (which fits well with the fixture_consumer in #339). The test_ prefix for the pytest plugin gets me every time :)