[Frontend] Scale Omni serving across API processes (#6923)

Signed-off-by: Sy03 <1370724210@qq.com>

tests/entrypoints/openai_api/test_video_server.py

@@ -463,6 +463,7 @@ async def test_server_worker_keeps_engine_alive_until_http_shutdown(monkeypatch)
 @pytest.fixture
 def test_client():
     app = FastAPI()
+    app.state.api_server_count = 1
     app.include_router(router)
     app.state.openai_serving_video = OmniOpenAIServingVideo.for_diffusion(
         diffusion_engine=FakeAsyncOmni(),
@@ -1804,6 +1805,7 @@ def test_action_extraction_accepts_multimodal_actions_payload():
 
 def test_missing_handler_returns_503():
     app = FastAPI()
+    app.state.api_server_count = 1
     app.include_router(router)
     app.state.openai_serving_video = None
     client = TestClient(app)
@@ -2790,6 +2792,7 @@ def test_cosmos3_control_upload_rejects_invalid_size(control_bytes, message, tes
 
 def test_sync_missing_handler_returns_503():
     app = FastAPI()
+    app.state.api_server_count = 1
     app.include_router(router)
     app.state.openai_serving_video = None
     client = TestClient(app)