Add comprehensive tests for mutual information processing and edge cases in CapacityAnalyzer

- Implement tests for processing SNR for mutual information with various modulators and channel types.
- Add tests for estimating mutual information with real signals and edge cases.
- Include tests for parallel processing and caching functionality.
- Enhance error handling tests for modulators and channels without state_dict.
- Validate numerical stability in binary entropy and MIMO capacity calculations.
- Cover additional edge cases and scenarios for complete test coverage.

Author: selimfirat