Switch from GPUGenerationWorker to AR worker with OmniARScheduler,
using the VoxCPM-style generator pattern for streaming:
- inference_stream() stored per-request in _stream_gens dict
- Each forward() call yields one audio chunk via next(generator)
- compute_logits() emits EOS only when last chunk is yielded
- AR scheduler loops until EOS, enabling progressive audio output
TTFP reduced from ~3.1s to ~0.11s (30x improvement).
Signed-off-by: Yueqian Lin <linyueqian@outlook.com>