[large-scale-serving] Integrate OmniCoordinator into stage engine pipeline (#3569)

Signed-off-by: chickeyton <ngton2014@gmail.com>
Signed-off-by: herotai214 <herotai214@gmail.com>
Co-authored-by: herotai214 <herotai214@gmail.com>

tests/diffusion/test_diffusion_engine_rpc_routing.py

@@ -136,6 +136,7 @@ def _make_engine_with_loop(
     calls and a real ``RequestScheduler``.
     """
     engine = DiffusionEngine.__new__(DiffusionEngine)
+    engine._closed = False
     engine.executor = _ConcurrencyTrackingExecutor(rpc_delay=rpc_delay)
 
     sched = RequestScheduler()
@@ -371,6 +372,7 @@ def test_collective_rpc_before_loop_starts_calls_executor_directly():
     on the caller's thread without enqueueing.
     """
     engine = DiffusionEngine.__new__(DiffusionEngine)
+    engine._closed = False
     engine._loop_started = False
     engine._rpc_lock = threading.RLock()
     engine._cv = threading.Condition(engine._rpc_lock)
@@ -391,6 +393,7 @@ def test_collective_rpc_before_loop_starts_serializes_concurrent_callers():
     serialize them so they cannot race on the shared executor MQ pair.
     """
     engine = DiffusionEngine.__new__(DiffusionEngine)
+    engine._closed = False
     engine._loop_started = False
     engine._rpc_lock = threading.RLock()
     engine._cv = threading.Condition(engine._rpc_lock)