[Perf] Eliminate Hop 3 IPC overhead for single-stage diffusion via inline execution (#2736)

Signed-off-by: samithuang <285365963@qq.com>
Signed-off-by: Samit <285365963@qq.com>

tests/engine/test_async_omni_engine_stage_init.py

@@ -100,10 +100,11 @@ def test_initialize_stages_passes_stage_init_timeout_to_diffusion_handshake(monk
     engine.log_stats = False
     engine.model = "dummy-model"
     engine.config_path = "dummy-config"
-    engine.num_stages = 1
+    engine.num_stages = 2
     engine.async_chunk = False
     engine.diffusion_batch_size = 1
     engine.single_stage_mode = False
+    engine._omni_master_server = None
     engine.stage_configs = [types.SimpleNamespace(stage_id=0, stage_type="diffusion", engine_args={})]
 
     metadata = types.SimpleNamespace(