[CI] Add Helion as an optional dependency

[gmagogsfm]

Related RFC

• This PR adds PyTorch Helion as an optional dependency to vLLM, this allows future Helion-based development and testing
• Developers can use pip install vllm[helion] to install vLLM variant with helion dependency
• Added a new CI job for Helion kernel-related tests
• Example import pattern

# Skip entire module if helion is not available
from vllm.utils.import_utils import has_helion
if not has_helion():
    pytest.skip(
        "Helion is not installed. Install with: pip install vllm[helion]",
        allow_module_level=True,
    )

import helion
import helion.language as hl

[gemini-code-assist]

Code Review

This pull request introduces Helion as an optional dependency, adding the necessary setup in setup.py, a utility function for checking its availability, and a smoke test. The CI configuration has also been updated to include tests for Helion. While the changes are generally well-implemented, I've identified a couple of improvements for the CI job configurations. Specifically, they reference a non-existent directory and could better leverage the new vllm[helion] extra for installation. My review includes suggestions to address these points.

[gmagogsfm]

@zou3519 @ProExpertProg Please take a look, let me know if this is the correct way of adding optional dependencies in vLLM. Thanks

[ProExpertProg]

This lookgs good to me, cc @mgoin @simon-mo for the release suffix

[yewentao256]

LGTM, thanks for the work!