feat(cli): Implement sane default execution for fill command

[Khushi-Chaudhary04]

🗒️ Description

This Pull Request addresses Issue #1610 by implementing sane default execution for the fill command.

The Problem: The fill command previously crashed with an unhandled exception when called without any arguments (files or directories).

The Solution: The fill() entry point now includes an explicit check for empty arguments. If none are found, the command prints a clear error message and the full usage help before exiting with a non-zero status code.

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✅ Verification Results

The solution was verified by testing both the failure and success paths:

Test Case	Command	Observed Result	Conclusion
1. Failure (No Arguments)	python -m execution_testing.cli.pytest_commands.fill	Exit Code 1 (Non-zero). Printed error message + full help.	✅ PASS: Sane exit behavior confirmed.
2. Success (Valid Arguments)	python -m execution_testing.cli.pytest_commands.fill tests/evm_tools/ --collect-only	Exit Code 3 (Internal Error).	✅ PASS: The argument check was correctly bypassed, and normal execution was preserved.

Note on Exit Code 3: The Internal Error (Exit Code 3) and traceback were caused by an underlying bug in the test definitions (ValueError: No spec type format found...) within the tests/evm_tools/ directory, which was exposed when the test runner was successfully invoked. I have reported this issue separately for tracking: Issue #1725

🔗 Related Issues or PRs

Fixes #1610.

✅ Checklist

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