[Diffusion] Add native paged KV backend for diffusion workers (#6102)

Signed-off-by: Acerak01-fy <wfy2003324@163.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/diffusion/test_diffusion_config_propagation.py

@@ -149,10 +149,18 @@ class TestCreateDefaultDiffusion:
         assert ea["enforce_eager"] is True
         assert ea["lora_path"] == "/tmp/lora"
 
-    def test_diffusion_kv_mode_roundtrip(self):
-        od = _roundtrip_diffusion_config(model="x", diffusion_kv_mode="paged_scheduler")
+    def test_diffusion_kv_mode_roundtrip(self, monkeypatch):
+        from vllm_omni.platforms import current_omni_platform
+
+        monkeypatch.setattr(current_omni_platform, "is_cuda", lambda: True)
+        od = _roundtrip_diffusion_config(
+            model="x",
+            diffusion_kv_mode="paged_scheduler",
+            diffusion_kv_max_rows_per_request=2,
+        )
 
         assert od.diffusion_kv_mode is DiffusionKVCacheMode.PAGED_SCHEDULER
+        assert od.diffusion_kv_max_rows_per_request == 2
 
     def test_diffusion_kv_sizing_fields_roundtrip(self, monkeypatch):
         monkeypatch.setattr(OmniDiffusionConfig, "_resolve_master_port", lambda self: 29500)