[Diffusion] Prepare HunyuanImage3 for Scheduler-managed paged KV cache (#5541)

Signed-off-by: zwhzzz0821 <zwhzzz0821@users.noreply.github.com>
Co-authored-by: zwhzzz0821 <zwhzzz0821@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

vllm_omni/diffusion/worker/utils.py

@@ -77,6 +77,9 @@ class StepRequestState:
     sampling: OmniDiffusionSamplingParams
     prompt: OmniPromptType | None = None
     kv_sender_info: dict | None = None
+    # Opaque model-owned preprocessing result. Scheduler-owned Diffusion KV
+    # request state is removed before this Worker state is built.
+    prepared_layout: Any | None = None
 
     # ── Encoded prompts (set once by prepare_encode) ──
     prompt_embeds: torch.Tensor | None = None