🗒️ Description

1. Adds an optional executionWitness field to the blockchain fixture base class.
2. Adds a new pytest plugin that:
   • pytest_addoption(): add a boolean --witness flag.
   • pytest_configure(): Compiles checks whether the witness-filler tool is in PATH if --witness is enabled; hard error if not.
   • Provides a fixture generate_witness that generates a fixture's execution witness using the witness-filler tool.
3. Calls the generate_witness fixture in BaseTestParametrizer. If --witness is not enabled, there is not change in fill behavior.

Usage

uv run fill tests/istanbul/eip1344_chainid/test_chainid.py --output=fixtures-witness --witness --clean

🔗 Related Issues or PRs

#2031

✅ Checklist

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

  uvx --with=tox-uv tox -e lint,typecheck,spellcheck,markdownlint

• 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).