feat: enhance tonal feature extraction and atonal detection in EssentiaAnalyzer

Commit notes

- Updated TonalFeatures model to include optional fields for is_tonal and tonality_strength. - Modified analyze_tonal method to detect atonal content using spectral flatness and entropy. - Improved key detection logic to return null for atonal content and adjusted confidence scaling accordingly. - Updated related interfaces and functions to handle new tonal feature attributes.

These changes aim to improve the accuracy of tonal analysis and provide better handling of atonal audio content.