[CI/UT][Refactor] Refactor multi-card CI

[MengqingCao]

What this PR does / why we need it?

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.9.1
• vLLM main: vllm-project/vllm@2e610de

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 52.33%. Comparing base (c30ddb8) to head (9f9e364).
Report is 81 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1645       +/-   ##
===========================================
+ Coverage   27.39%   52.33%   +24.93%     
===========================================
  Files          56       78       +22     
  Lines        6191     9638     +3447     
===========================================
+ Hits         1696     5044     +3348     
- Misses       4495     4594       +99     

Flag	Coverage Δ
unittests	52.33% <ø> (+24.93%)	⬆️

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