[CI] Add pytest markers to current tests and update the doc. (#577)

Signed-off-by: Alicia <115451386+congw729@users.noreply.github.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/entrypoints/test_omni_new_request_data.py

@@ -1,9 +1,12 @@
 from types import SimpleNamespace
 
+import pytest
 import torch
 
 from vllm_omni.core.sched.output import OmniNewRequestData
 
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
 
 def test_omni_new_request_data_copies_payloads():
     prompt_embeds = torch.randn(2, 3)