Enhance multi-lead ECG extraction and beat validation pipeline
- Added dual-lead ECG processing support for feature extraction testing
- Updated lead buffer assignment to use independent lead data sources
- Increased ECG processing window from 512 to 768 samples
- Added per-lead feature reporting loop with dynamic lead indexing
- Added beat data validation using m_data_available flag
- Added fallback handling for invalid or incomplete beat extraction
- Added rhythm segment boundary tracking for P and T wave indices
- Added waveform availability state propagation across extraction stages
- Added rhythm waveform segment buffering for downstream analysis
- Optimized required sample threshold calculation using cached size_t value
- Fixed incorrect WaveletRegistry mappings for COIF2 and COIF3 filters
- Added beat-level metadata for waveform start/end indices
- Improved rhythm analysis state tracking and extraction consistency
- Refactored extraction logic to avoid storing incomplete annotation results
- Cleaned formatting and removed obsolete commented code paths