Add NebiusLLMService for Nebius Token Factory

Adds an OpenAI-compatible LLM service for Nebius Token Factory, supporting
open-source models (Meta Llama, Qwen, DeepSeek) via their OpenAI-compatible
REST API at https://api.tokenfactory.nebius.com/v1/.

pyproject.toml

@@ -65,6 +65,7 @@ cerebras = []
 daily = [ "daily-python~=0.27.0" ]
 deepgram = [ "deepgram-sdk>=6.1.1,<7", "pipecat-ai[websockets-base]" ]
 deepseek = []
+nebius = []
 elevenlabs = [ "pipecat-ai[websockets-base]" ]
 fal = []
 fireworks = []