Add Smallest AI TTS service integration

Adds SmallestTTSService, a WebSocket-based TTS service using Smallest AI's
Lightning v3.1 model. Follows current Pipecat service conventions:

- SmallestTTSSettings dataclass with runtime-updatable settings (voice,
  language, speed, etc.)
- Reconnects on model change; keepalive every 30s to prevent idle timeout
- TTS settings default to None so the API applies its own defaults
- Model enum: SmallestTTSModel.LIGHTNING_V3_1

Includes a foundational example (07zl-interruptible-smallest.py) using
Deepgram STT + Smallest TTS + OpenAI LLM.

STT integration will follow in a separate PR once the hallucination/finalize
behaviour is resolved.

Made-with: Cursor

pyproject.toml

@@ -111,6 +111,7 @@ runner = [ "python-dotenv>=1.0.0,<2.0.0", "uvicorn>=0.32.0,<1.0.0", "fastapi>=0.
 sagemaker = ["aws_sdk_sagemaker_runtime_http2; python_version>='3.12'"]
 sambanova = []
 sarvam = [ "sarvamai==0.1.26", "pipecat-ai[websockets-base]" ]
+smallest = [ "pipecat-ai[websockets-base]" ]
 sentry = [ "sentry-sdk>=2.28.0,<3" ]
 silero = []
 simli = [ "simli-ai~=2.0.1"]