feat(pytest): enable piping of fill's json to consume rlp

[danceratopz]

🗒️ Description

This allows a user to pipe the JSON generated by fill directly to consume rlp without writing any intermediate files.

For example:

fill --output=stdout --fork=Merge | consume rlp -v

This is bit tricky as both commands are pytest-based and pytest is not designed for this purpose. Therefore, the click interface modifies command-line options:

• for fill based on whether --output=stdout is set (in order to get pytest to not output anything else on its stdout). I didn't manage to add flags dynamically within a plugin. But perhaps this method is less hacky??! 🤣
• for consume rlp if it detects that it's receiving input on stdin.

🔗 Related Issues

This could be an alternative solution to ethereum#324.

✅ Checklist

These should be ticked off in the main PR in execution-spec-tests: https://github.com/ethereum/execution-spec-tests/discussions

• 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.