[XPU] allow custom workers (e.g. vllm-omni workers) to be used on XPU (#30935)

Signed-off-by: Fanli Lin <fanli.lin@intel.com>

vllm/platforms/xpu.py

@@ -159,7 +159,10 @@ class XPUPlatform(Platform):
 
         # check and update parallel config
         parallel_config = vllm_config.parallel_config
-        parallel_config.worker_cls = "vllm.v1.worker.xpu_worker.XPUWorker"
+        # Only override worker_cls if it's still the default "auto"
+        # This allows custom workers (like vllm-omni workers) to be used on XPU
+        if parallel_config.worker_cls == "auto":
+            parallel_config.worker_cls = "vllm.v1.worker.xpu_worker.XPUWorker"
         if vllm_config.kv_transfer_config is not None:
             vllm_config.kv_transfer_config.enable_permute_local_kv = True