[Core] Asynchronous Output Processor (#7049)

Co-authored-by: Alexander Matveev <alexm@neuralmagic.com>

tests/multi_step/test_correctness_async_llm.py

@@ -62,6 +62,9 @@ async def test_multi_step(example_prompts, model: str, tp_size: int,
     ms_server_args = DEFAULT_SERVER_ARGS + \
         ["--num-scheduler-steps", f"{num_scheduler_steps}"]
 
+    # Disable output proc callback as its not supported
+    # with multi-step right now
+    ms_server_args += ["--disable-async-output-proc"]
     if eager_mode:
         ms_server_args.append("--enforce-eager")