[Misc] Add warning for incompatible Ray backend with ACL Graph mode

[22dimensions]

What this PR does / why we need it?

cherry-pick #1501 from 0.9.1-dev to main

Currently, Ray is not compatible with ACL Graph, so we need to fall back to eager mode when using the Ray backend.

co-authored: Yizhou Liu liu_yizhou@outlook.com

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.10.0
• vLLM main: vllm-project/vllm@2836dd7

[github-actions]

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[Yikun]

Please rename title and commits msg more meaningful.

[22dimensions]

Please rename title and commits msg more meaningful.

done

[Yikun]

LGTM if CI passed

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.03%. Comparing base (72eceff) to head (754d42b).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
vllm_ascend/platform.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2132      +/-   ##
==========================================
+ Coverage   74.41%   75.03%   +0.62%     
==========================================
  Files         100      103       +3     
  Lines       11208    11358     +150     
==========================================
+ Hits         8340     8523     +183     
+ Misses       2868     2835      -33     

Flag	Coverage Δ
unittests	75.03% <33.33%> (+0.62%)	⬆️

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