[Test] Add unittests for vllm_ascend

[SunnyLee151064]

What this PR does / why we need it?

This PR contains some unit tests for vllm ascend.

Does this PR introduce any user-facing change?

No

How was this patch tested?

• vLLM version: v0.9.2
• vLLM main: vllm-project/vllm@d978410

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[codecov]

Codecov Report

Attention: Patch coverage is 99.23599% with 9 lines in your changes missing coverage. Please review.

Project coverage is 67.99%. Comparing base (c30ddb8) to head (59398c6).
Report is 160 commits behind head on main.

Files with missing lines	Patch %	Lines
...ut/distributed/device_communicators/test_pyhccl.py	87.50%	7 Missing ⚠️
tests/ut/core/test_scheduler.py	99.34%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1662       +/-   ##
===========================================
+ Coverage   27.39%   67.99%   +40.59%     
===========================================
  Files          56       85       +29     
  Lines        6191     9613     +3422     
===========================================
+ Hits         1696     6536     +4840     
+ Misses       4495     3077     -1418     

Flag	Coverage Δ
unittests	67.99% <99.23%> (+40.59%)	⬆️

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