[Diffusion] Add loader-owned host-weight plans for DLO (TP=1) (#6213)

Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/diffusion/test_diffusion_model_runner.py

@@ -740,6 +740,9 @@ def test_load_model_clears_cache_backend_for_unsupported_pipeline(monkeypatch):
             del kwargs
             return SimpleNamespace(transformer=torch.nn.Identity())
 
+        def take_host_weight_plan(self):
+            return None
+
     class _DummyMemoryProfiler:
         consumed_memory = 0
 
@@ -779,7 +782,11 @@ def test_load_model_clears_cache_backend_for_unsupported_pipeline(monkeypatch):
     monkeypatch.setattr(model_runner_module, "LoadConfig", lambda: object())
     monkeypatch.setattr(model_runner_module, "DiffusersPipelineLoader", _DummyLoader)
     monkeypatch.setattr(model_runner_module, "DeviceMemoryProfiler", _DummyMemoryProfiler)
-    monkeypatch.setattr(model_runner_module, "get_offload_backend", lambda od_config, device: None)
+    monkeypatch.setattr(
+        model_runner_module,
+        "get_offload_backend",
+        lambda od_config, device, host_weight_plan: None,
+    )
     monkeypatch.setattr(
         model_runner_module, "get_cache_backend", lambda cache_backend, cache_config: dummy_cache_backend
     )