[Refactor] Nixl util using lazy init

[yewentao256]

Summary

• make vllm.distributed.nixl_utils resolve optional NIXL / RIXL symbols lazily
• avoid triggering NIXL-related import side effects during module import
• update EPLB NIXL access to fetch symbols through nixl_utils at runtime
• avoid duplicate logs

INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available
INFO 04-29 21:05:22 [nixl_utils.py:32] NIXL is available

[claude]

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[mergify]

Hi @yewentao256, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

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Tip

Is mypy failing?

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# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10

[gemini-code-assist]

Code Review

This pull request refactors the nixl_utils module to implement lazy loading of NIXL and RIXL dependencies using getattr. This change ensures that these modules are only imported upon access and that necessary environment variables are configured immediately prior to loading. The eplb_communicator.py file was updated to use the new module-level access pattern. I have no feedback to provide as there were no review comments to evaluate.