Refactor code structure for improved readability and maintainability

Implement enhanced pronunciation assessment system with Wav2Vec2 support

feat: refactor Wav2Vec2 character ASR to support quantization and improve model loading

feat: implement Wav2Vec2 character-level ASR with ONNX and Transformers support, add phoneme comparison and feedback generation

fix: update import statement for BaseModel in agent.py and add timing logs in speaking_controller.py

Add Wav2Vec2 model conversion and inference to ONNX format