Fix vllm nccl sync error

[pan-x-c]

Description

As the title says

Checklist

Please check the following items before code is ready to be reviewed.

• Code has passed all tests
• Docstrings have been added/updated in Google Style
• Documentation has been updated
• Code is ready for review

[gemini-code-assist]

Summary of Changes

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This pull request addresses a vllm NCCL synchronization error by activating a previously commented-out import statement. The change ensures that the vllm library is loaded, which implicitly configures the environment to prevent common distributed communication issues related to CUDA memory management, thereby fixing the reported error.

Highlights

• NCCL Sync Error Fix: Enabled the import of the vllm library in trinity/trainer/verl/fsdp_workers.py. This import is intended to automatically set the NCCL_CUMEM_ENABLE environment variable, which is crucial for resolving NCCL synchronization issues, particularly in distributed training environments.

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[gemini-code-assist]

Code Review

This PR fixes an NCCL sync error by uncommenting an import of vllm to leverage its side-effects. I've suggested making this fix more explicit and maintainable by setting the required environment variable directly.