Handle optional bool-or-string CLI args in get_kwargs

[cvan20191]

Why

This PR moves bool | str | None CLI handling from a local argparse special case for --hf-token into get_kwargs(), so generated kwargs can handle the field directly without a manual override.

What changed

• Added bool | str | None handling in get_kwargs().
• Removed the local --hf-token argparse special case.
• Added regression coverage for get_kwargs(ModelConfig)["hf_token"].
• Added CLI parser coverage for the existing --hf-token behavior.

Behavior preserved

• No flag parses as None.
• --hf-token parses as True.
• --hf-token TOKEN parses as "TOKEN".
• --hf-token None parses as "None".

Verification

• .venv/bin/python -m pytest tests/engine/test_arg_utils.py -v (72 passed)
• pre-commit run ruff-format --files vllm/engine/arg_utils.py tests/engine/test_arg_utils.py
• pre-commit run ruff-check --files vllm/engine/arg_utils.py tests/engine/test_arg_utils.py
• git diff --check

Checked open/closed PRs for duplicate—no matches. Used AI to generate draft tests, but manually reviewed

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[gemini-code-assist]

Code Review

This pull request automates the handling of CLI arguments that can be either a boolean or a string, specifically targeting the bool | str | None type hint pattern. The logic in vllm/engine/arg_utils.py was updated to configure these arguments with nargs='?' and const=True, allowing for cleaner integration of the --hf-token flag. New tests were implemented in tests/engine/test_arg_utils.py to verify the argument parsing behavior. I have no feedback to provide.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[cvan20191]

Hi @DarkLight1337, would you or someone from the team mind taking a look at this when you get a chance?

[hmellor]

LGTM!

[cvan20191]

@hmellor CI flaked on elastic-ep-scaling-test (GSM8K accuracy). Expected 0.58; got ~0.558 (scaling) / ~0.519 (uneven).

I rebased onto main, and this patch doesn’t touch that codepath. Could you re-trigger Buildkite or re-enable auto-merge? Build: #64150

(cc @DarkLight1337 for visibility)

[cvan20191]

@hmellor friendly ping on this when you have a chance. It looks like the remaining failure is still the unrelated elastic-ep-scaling-test flake after the rebase. Could someone re-enable auto-merge or retrigger CI? Thank you