[Misc] Deprecation Warning when setting --engine-use-ray

[wallashss]

Fix #7045

This PR adds a deprecation warning when users set --engine-use-ray.
For a concise message, I added in the message the issue number for additional clarification.

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[youkaichao]

we can hard fail here, and put an env var to turn it on with a warning.

something like:

if self.engine_use_ray:
    if envs.VLLM_ALLOW_ENGINE_USE_RAY:
        # print warning
    else:
        # directly error, with the error message pointing to the RFC issue

for the link, please use full url.

[wallashss]

Thank you for your comment @youkaichao. I added modifications to address your suggestions.

[youkaichao]

LGTM, thanks for the contribution!

[njhill]

Thanks @wallashss!

Unfortunately some of the tests make use of this arg, we should update the tests to not use it.

If we want to get this PR merged in the meantime, we'll have to include changes to add the override env var to the tests in question.

[youkaichao]

we can run these tests with the override env var. we don't need to remove them right now.

[njhill]

we can run these tests with the override env var. we don't need to remove them right now.

I think it is mostly tests for other things that make use of --engine-use-ray rather than tests for this option in itself, so we'll probably want to rework rather than remove them (agree that can be follow-on work though).

[njhill]

Thanks @wallashss... just some minor change suggestions to the wording

[youkaichao]

hope @wallashss put the env var in all relevant places and the full test can pass 😉

[wallashss]

hope @wallashss put the env var in all relevant places and the full test can pass 😉

I hope so too! I checked the tests and after several fixes, I did not find errors related to my changes. Right now I solved a conflict and a code format error. I guess that will be ready in the next round of checks.

[youkaichao]

tests look unrelated. merging.

[wallashss]

Thank you @youkaichao!