feat(diffusion): add request-gated VAE fast paths

Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>

vllm_omni/engine/arg_utils.py

@@ -491,6 +491,7 @@ class OrchestratorArgs:
     step_execution: bool = False
     vae_use_slicing: bool = False
     vae_use_tiling: bool = False
+    vae_decode_precision: str | None = None
     enable_multithread_weight_load: bool = True
     num_weight_load_threads: int = 4
     enable_cpu_offload: bool = False

vllm_omni/engine/async_omni_engine.py

@@ -1026,6 +1026,7 @@ class AsyncOmniEngine:
             "request_batch_max_wait_ms": kwargs.get("request_batch_max_wait_ms", 0.0),
             "vae_use_slicing": kwargs.get("vae_use_slicing", False),
             "vae_use_tiling": kwargs.get("vae_use_tiling", False),
+            "vae_decode_precision": kwargs.get("vae_decode_precision", None),
             "cache_backend": cache_backend,
             "cache_config": cache_config,
             "enable_cache_dit_summary": kwargs.get("enable_cache_dit_summary", False),