[CI] Restructure vLLM-Omni Test Layout, Fixture Scope, and Support Modules (#2620)

Signed-off-by: wangyu <410167048@qq.com>

tests/diffusion/distributed/test_ulysses_uaa_perf.py

@@ -17,7 +17,7 @@ import pytest
 import torch
 import torch.distributed as dist
 
-from tests.utils import hardware_test
+from tests.helpers.mark import hardware_test
 from vllm_omni.diffusion.attention.parallel.ulysses import (
     _all_gather_int,
     _ulysses_all_to_all_any_o,