[CI] Upgrade vLLM to 20250920 (c60e613) and address config break

[Yikun]

What this PR does / why we need it?

Bump main to vllm-project/vllm@c60e613

• Updated imports in vllm.config to vllm.config.model(vllm-project/vllm@aed1687) Move ModelConfig from config/__init__.py to config/model.py vllm#25252

• Refactored vllm_ascend/sample/sampler.py to use string values for logprobs_mode instead of the LogprobsMode enum, simplifying logprobs mode handling and improving compatibility with recent vLLM changes (vllm-project/vllm@aed1687) Move ModelConfig from config/__init__.py to config/model.py vllm#25252

Does this PR introduce any user-facing change?

No

How was this patch tested?

CI passed

• vLLM version: v0.10.2
• vLLM main: vllm-project/vllm@6d8246a

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 42.85714% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.93%. Comparing base (1bbb20e) to head (230d695).
⚠️ Report is 80 commits behind head on main.

Files with missing lines	Patch %	Lines
vllm_ascend/sample/sampler.py	42.85%	8 Missing ⚠️

❌ Your patch status has failed because the patch coverage (42.85%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3067      +/-   ##
==========================================
- Coverage   74.76%   71.93%   -2.84%     
==========================================
  Files         150      168      +18     
  Lines       20891    23554    +2663     
==========================================
+ Hits        15620    16944    +1324     
- Misses       5271     6610    +1339     

Flag	Coverage Δ
unittests	71.93% <42.85%> (-2.84%)	⬇️

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[Yikun]

 UnboundLocalError: cannot access local variable 'raw_logprobs' where it is not associated with a value

https://github.com/vllm-project/vllm-ascend/actions/runs/17881166432/job/50849001999?pr=3067

[Yikun]

>>> from enum import Enum
>>> class Color(Enum):
...     RED = "red"
...     GREEN = "green"
...     BLUE = "blue"
...
>>> Color.RED
<Color.RED: 'red'>
>>> Color.RED=="red"
False
>>>

Here is the note why we need this