Return VAD sentence timestamps for SenseVoice

[LauraGPT]

Summary

• return per-VAD sentence_info when sentence_timestamp=True and an ASR model such as SenseVoice has no token timestamps
• preserve punctuation-based segmentation and timestamp-capable ASR behavior
• include both text and sentence fields for downstream compatibility

Validation

• 30 passed across VAD/punctuation, subtitle, CLI, and OpenAI server segment tests
• real iic/SenseVoiceSmall CPU inference on asr_example.wav: VAD sentence 610-5530 ms, recognized expected Chinese text
• py_compile and git diff --check pass

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.