- Added `XAISTTService` for real-time speech-to-text using xAI's voice STT WebSocket API (`wss://api.x.ai/v1/stt`). Streams raw audio (PCM, µ-law, or A-law) and emits interim and final transcription frames driven by the server's `is_final` / `speech_final` flags. Settings expose `interim_results`, `endpointing`, `language`, `multichannel`, `channels`, and `diarize`. Requires the `xai` optional extra (`pip install "pipecat-ai[xai]"`).
