[Chore]: refactor out unused/redundant params in diffusion pipelines (#1235)

Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/design/feature/cfg_parallel.md

@@ -126,16 +126,16 @@ Call `self.diffuse` in your pipeline's forward function:
 
 ```python
 import torch.nn as nn
+from vllm_omni.diffusion.worker.request_batch import DiffusionRequestBatch
+
 class YourModelPipeline(nn.Module, CFGParallelMixin):
     def forward(
         self,
-        prompt: str,
-        negative_prompt: str | None = None,
-        guidance_scale: float = 3.5,
-        num_inference_steps: int = 50,
-        **kwargs,
-    ):
-        # Encode prompts, Initialize latents, Get timesteps
+        req: DiffusionRequestBatch,
+    ) -> list[DiffusionOutput]:
+        # Read prompts and sampling params from the request
+        ...
+        # Encode prompts, initialize latents, get timesteps
         ...
         # Run diffusion loop (calls the mixin's diffuse method)
         latents = self.diffuse(