[Refactor][Diffusion] Resolve distributed layerwise topology in the plan (#7326)

Signed-off-by: specture724 <specture724@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/diffusion/models/magi2/test_native_dlo_allgather.py

@@ -36,6 +36,7 @@ from vllm_omni.diffusion.offloader.distributed_layerwise_backend import (
     DistributedLayerwiseOffloadBackend,
     DistributedLayerwiseOffloadHook,
 )
+from vllm_omni.diffusion.offloader.plan_resolver import ResolvedComponent
 
 
 @dataclass(frozen=True)
@@ -46,12 +47,6 @@ class _WeightSourceStub:
     prefix: str
 
 
-@dataclass(frozen=True)
-class _PipelineModulesStub:
-    dits: list[nn.Module]
-    dit_names: list[str]
-
-
 _WORLD_SIZE = 4
 pytestmark = [pytest.mark.diffusion, pytest.mark.cpu, pytest.mark.core_model]
 
@@ -189,7 +184,7 @@ def _load_mmap_transform_and_reconstruct(
         backend._mmap_transforms_by_tensor_id = {}
         backend._load_weights_via_mmap(
             pipeline,
-            _PipelineModulesStub(dits=[target], dit_names=["transformer"]),
+            (ResolvedComponent(path="transformer", module=target, selected=True),),
             plan_result.plan,
         )