test(frozen_dataclass_sealable): Enhance test suite maintainability and clarity

why: Improve the test suite for better maintainability, clarity, and documentation.
what:
- Added reusable pytest fixtures for common test class patterns
- Created parameterized tests for circular references and container types
- Enhanced test documentation with detailed docstrings
- Added TODOs with GitHub issue references for skipped tests
- Refactored existing tests to reduce code duplication
- Standardized test patterns and assertions

The improved test suite maintains comprehensive coverage while being easier to understand and extend.

Author: tony