[Core] Allow specifying custom Executor (#6557)

vllm/executor/cpu_executor.py

@@ -17,6 +17,8 @@ logger = init_logger(__name__)
 
 class CPUExecutor(ExecutorBase):
 
+    uses_ray: bool = False
+
     def _init_executor(self) -> None:
         assert self.device_config.device_type == "cpu"
         assert self.lora_config is None, "cpu backend doesn't support LoRA"