- Add library configuration to support both lib and binary targets
- Implement unified error handling with NCBError throughout the codebase
- Add circuit breaker pattern for external API calls (Voicevox, GCP TTS)
- Introduce comprehensive performance metrics and monitoring
- Add cache persistence with disk storage support
- Implement retry mechanism with exponential backoff
- Add configuration file support (config.toml) with env var fallback
- Enhance logging with structured tracing (debug, warn, error levels)
- Add extensive unit tests for cache, metrics, and circuit breaker
- Update base64 decoding to use modern API
- Improve API error handling for Voicevox and GCP TTS clients
Breaking changes:
- Function signatures now return Result<T, NCBError> instead of panicking
- Cache key structure modified with serialization support
