fix: resolve CI failures in governance validator and tests
- Refactor `tests/test_governance_validator.py` to reduce duplication (JSCPD).
- Fix imports and formatting in `tests/test_governance_validator.py` (isort, black, flake8).
- Change `ValidationSummary` to `dict` in `tools/validate_ai_governance_artifacts.py` to allow dynamic key access (mypy).
- Ensure valid hex hashes in duplicate evidence hash test.
Co-authored-by: OneFineStarstuff <87420139+OneFineStarstuff@users.noreply.github.com>