test: add comprehensive integration tests for new Direct API methods

- Add tests for create_redactions (preset/regex/text strategies)
- Add tests for optimize_pdf with various options
- Add tests for password_protect_pdf and permissions
- Add tests for set_pdf_metadata
- Add tests for apply_instant_json and apply_xfdf
- Include error case testing for validation

All tests follow existing patterns and will run with live API when configured.

Author: jdrhyne