[diffusion][feature] Add component-selective offload policies (#5929)

Signed-off-by: lishunyang12 <lishunyang12@163.com>

tests/diffusion/models/sana_video/test_cache_offload.py

@@ -16,7 +16,7 @@ from tests.diffusion.models.sana_video.test_transformer_sana_video import (  # n
     _TINY_CONFIG,
     _init_distributed,
 )
-from tests.diffusion.offloader.test_layerwise_backend import DummyEvent, DummyStream, dummy_stream
+from tests.diffusion.offloader.helpers import DummyEvent, DummyStream, dummy_stream
 from vllm_omni.diffusion.attention import selector as attention_selector
 from vllm_omni.diffusion.attention.backends.sdpa import SDPABackend
 from vllm_omni.diffusion.cache.cachedit import CacheDiTBackend
@@ -226,7 +226,7 @@ def test_component_loading_uses_loader_device_not_runtime_device(monkeypatch):
     monkeypatch.setattr(
         pipeline_module,
         "_load_json",
-        lambda _model, filename, _local: ({"vae": [None, "FakeVAE"]} if filename == "model_index.json" else {}),
+        lambda _model, filename, _local: {"vae": [None, "FakeVAE"]} if filename == "model_index.json" else {},
     )
     monkeypatch.setattr(
         pipeline_module,