[Refactor]: clean up diffusion scheduler interfaces (#5216)

Signed-off-by: Huang, Zeyu <11222265+fhfuih@users.noreply.github.com>
Signed-off-by: Zeyu Huang | 黃澤宇 <11222265+fhfuih@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

tests/diffusion/test_input_batch_txt_seq_lens.py

@@ -2,14 +2,14 @@ import pytest
 import torch
 
 from vllm_omni.diffusion.worker.input_batch import _prepare_request_prompt_field
-from vllm_omni.diffusion.worker.utils import DiffusionRequestState
+from vllm_omni.diffusion.worker.utils import StepRequestState
 from vllm_omni.inputs.data import OmniDiffusionSamplingParams
 
-pytestmark = [pytest.mark.cpu]
+pytestmark = [pytest.mark.core_model, pytest.mark.diffusion, pytest.mark.cpu]
 
 
 def test_prepare_request_prompt_field_refreshes_txt_seq_lens_after_padding():
-    state = DiffusionRequestState(
+    state = StepRequestState(
         request_id="req-0",
         sampling=OmniDiffusionSamplingParams(),
         prompt_embeds=torch.randn(1, 10, 4),