1. auto_model.py: When ASR model (e.g. SenseVoice) doesn't produce
timestamps, automatically fall back to vad_segment mode for speaker
diarization instead of crashing. Fixes#2945.
2. load_utils.py: Add soundfile as fallback when torchaudio.load fails
(torchaudio>=2.11 requires torchcodec). Falls through to ffmpeg only
if soundfile also fails.