- Added enhancements to `NvidiaTTSService`:

  - Cross-sentence stitching: multiple sentences within an LLM turn are fed into a single `SynthesizeOnline` gRPC stream for seamless audio across sentence boundaries (requires Magpie TTS model v1.7.0+).
  - `custom_dictionary` and `encoding` parameters for IPA-based custom pronunciation and output audio encoding.
  - Metrics generation (`can_generate_metrics` returns true) and `stop_all_metrics()` when an audio context is interrupted.
  - gRPC error handling around synthesis config retrieval (`GetRivaSynthesisConfig`).