Re-enable seed for pipeline parallel

[njhill]

This reverts commit 0f7df61.

This should be merged once we're including vllm-project/vllm#6698 in the corresponding vllm. That one should be merged to upstream imminently.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.36%. Comparing base (09290e6) to head (ee33319).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   61.29%   61.36%   +0.07%     
==========================================
  Files          20       20              
  Lines        1186     1183       -3     
  Branches      210      209       -1     
==========================================
- Hits          727      726       -1     
+ Misses        383      382       -1     
+ Partials       76       75       -1     

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