[Diffusion] Address DLO host cache review feedback

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

vllm_omni/diffusion/model_loader/host_weight_plan.py

@@ -42,6 +42,7 @@ class HostWeightPlan:
     planned_source_prefixes: frozenset[str] = frozenset()
     runtime_layout_key: str | None = None
     post_load_complete: bool = False
+    expected_file_digests: dict[str, str] | None = None
 
 
 @dataclass(frozen=True)