Add a new audio_tokenizer_device input on MOSSTTSLoader (auto/cuda/cpu).
auto mirrors the main model's device (previous behaviour). cpu keeps the
audio tokenizer on host RAM, saving ~1-3 GB of VRAM at the cost of some
CPU latency at the start (encoding the reference clip) and end (decoding
the generated codes) of each generation.
Useful on 16-20 GB GPUs where MOSS-TTS' main model + activations push
right against the ceiling. Including the audio_tokenizer_device in the
cache key prevents stale entries when a user toggles the setting.