chore: Remove unused test files and build artifacts

- Delete unused conftest_new.py duplicate test configuration
- Remove stale test_shell_executor_redirections.py.bak backup file
- Clean up empty test directories (unit/, validators/) and cache files
- Maintain 100% test functionality with 120 passing tests

This cleanup improves repository hygiene without affecting any functionality.
All tests continue to pass and code quality metrics are preserved.

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

Author: tumf