Remove stale riva mock imports from autodoc_mock_imports since the riva
service was removed and nvidia-riva-client is installed during doc builds.
Add pipecat.turns and pipecat.extensions to import_core_modules() and
add Turns to the index.rst toctree. Regenerate uv.lock to reflect the
riva extra removal from pyproject.toml.
Adds support for using Ultravox Realtime as a speech-to-speech service.
Also removes the deprecated Ultravox speech-to-text vllm model integration to avoid confusion.
