Relax protobuf library version constraints

[jeffreywang-anyscale]

Purpose

Relaxes the strict version pins for protobuf, grpcio, and grpcio-reflection introduced in #30190 (gRPC server entrypoint). This allows vLLM to work with a wider range of protobuf versions while maintaining compatibility.

Ray is upgrading vLLM to 0.14.0, but there are other dependencies in Ray conflicting with the protobuf version that vLLM requires (>=6.30.0) starting from the introduction of #30190. It's because that some other libraries that ray depends on require an older version of protobuf. For example with tensorflow, we run into such errors:

tensorflow 2.15.1 depends on protobuf!=4.21.0, !=4.21.1, !=4.21.2, !=4.21.3, !=4.21.4, !=4.21.5, <5.0.0dev and >=3.20.3

Test Plan & Result

Verified that installing common.txt with uv pip install -r requirements/common.txt in a clean conda environment resolves to the same versions with and without the constraints.

• With

protobuf==6.33.4
grpcio==1.76.0

• Without

protobuf==6.33.4
grpcio==1.76.0

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request correctly refactors the grpc-server dependencies into an optional extra requirement, which can be installed via pip install vllm[grpc-server]. This is achieved by moving the protobuf version constraint from requirements/common.txt to a new grpc-server extra in setup.py. A runtime check has been added to grpc_server.py to ensure the required protobuf version is installed, providing a clear error message if it's not. The implementation is clean and effective. I've added one high-severity comment to improve the robustness of the version check by handling a potential AttributeError.

[jeffreywang-anyscale]

cc: @njhill @eicherseiji @kouroshHakha

[eicherseiji]

Thanks @jeffreywang-anyscale and @njhill!