[Core] Add batch parallel VAE decode (#8162)

Signed-off-by: QianCyrus <101633534+QianCyrus@users.noreply.github.com>

vllm_omni/diffusion/distributed/autoencoders/distributed_vae_executor.py

@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
 
 from __future__ import annotations
 
@@ -177,8 +177,14 @@ class DistributedVaeMixin:
         self.distributed_executor.set_parallel_size(parallel_size, mode=mode)
 
     def is_distributed_enabled(self) -> bool:
+        """Whether to use distributed tile/patch execution, not native tiling.
+
+        Batch decode has its own dispatch; in batch mode, encoding and each
+        assigned image chunk keep the native tiling/slicing settings.
+        """
         if (
             self.distributed_executor.parallel_size <= 1
+            or self.distributed_executor.parallel_mode == "batch"
             or not dist.is_initialized()
             or not getattr(self, "use_tiling", False)
         ):