fix(xai): expose TTS websocket options

[nightcityblade]

Fixes #6077

Summary

• expose xAI TTS websocket options for optimize_streaming_latency, speed, and text_normalization
• forward provided values as websocket query parameters
• allow updating these options via update_options

Testing

• uv run ruff format livekit-plugins/livekit-plugins-xai/livekit/plugins/xai/tts.py
• uv run ruff check livekit-plugins/livekit-plugins-xai/livekit/plugins/xai/tts.py
• uv run python - <<'PY' ... xAI TTS option smoke test

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[nightcityblade]

Thanks for the review. I pushed f38e7d5 to forward the new xAI TTS WebSocket options (optimize_streaming_latency, speed, text_normalization) as query params, and changed the WebSocket connection helper to use the stream's captured options snapshot so changes made after stream creation don't leak into that stream's connection.