feat: add Inception LLM service with Mercury-2 support

Adds InceptionLLMService, an OpenAI-compatible service for Inception's
Mercury-2 diffusion-based reasoning model. Supports reasoning_effort
(instant/low/medium/high) and realtime mode for reduced TTFT.

pyproject.toml

@@ -77,6 +77,7 @@ groq = [ "groq>=0.23.0,<2" ]
 gstreamer = [ "pygobject~=3.50.0" ]
 heygen = [ "livekit>=1.0.13,<2", "pipecat-ai[websockets-base]" ]
 hume = [ "hume>=0.11.2,<1" ]
+inception = []
 inworld = [ "pipecat-ai[websockets-base]" ]
 koala = [ "pvkoala~=2.0.3" ]
 kokoro = [ "kokoro-onnx>=0.5.0,<1", "requests>=2.32.5,<3" ]