CI: Pin linter versions in CONTRIBUTE.md and update pre-commit hook

[gyohuangxin]

Summary

• Update recommended linter versions in CONTRIBUTE.md to match current CI:
  • black: 25.1.0 → 26.3.0
  • ruff: 0.11.11 → 0.15.7
  • clang-format: specify version 18 (18/19/20 are all supported)
• Update .githooks/pre-commit to prefer versioned clang-format-{20,19,18} with fallback to unversioned clang-format

This ensures local dev environments stay consistent with CI, avoiding format mismatches that cause CI failures.

Test plan

• Verify pre-commit hook finds clang-format-18 on dev machines
• Verify black==26.3.0 and ruff==0.15.7 produce same results as CI

[github-actions]

🏷️ CI Guide

Runs automatically on every PR:

• ✅ Pre-checks (submodule verification, code formatting)
• ✅ Aiter op tests (gfx942 + gfx950)
• ✅ Triton tests (only when aiter/ops/triton/** or related paths are changed)

Extended tests (opt-in via labels):

Label	Tests
ci:sglang	SGLang integration tests
ci:atom	ATOM benchmark (DeepSeek-R1 + GPT-OSS)
ci:vllm	vLLM benchmark
ci:all	All of the above

Add labels via the sidebar or gh pr edit 2448 --add-label <label>

[Copilot]

Pull request overview

Updates contributor tooling guidance and the repo’s git pre-commit hook to reduce formatting mismatches between local development environments and CI, especially around clang-format selection.

Changes:

• Update CONTRIBUTE.md recommended black/ruff versions and specify clang-format v18 (noting 18/19/20 support).
• Enhance .githooks/pre-commit to prefer clang-format-{20,19,18} and fall back to unversioned clang-format.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
CONTRIBUTE.md	Updates documented linter versions/commands to align local formatting with expected CI behavior.
.githooks/pre-commit	Adds version-aware clang-format discovery with a fallback to the unversioned binary.

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[Copilot]

CONTRIBUTE.md now pins black/ruff versions as “match current CI”, but CI currently runs psf/black@stable (not a specific version) and installs ruff without a version pin in .github/workflows/pre-checks.yaml. This can still lead to local/CI mismatches when CI updates. Consider either pinning CI to the same versions or rewording this section as “recommended versions” and documenting how to check the versions used in CI.

[Copilot]

The skip message is slightly inaccurate: the script also checks for unversioned clang-format, but the message only mentions (18/19/20). Consider updating it to something like “clang-format not found (tried clang-format-20/19/18 and clang-format)” so it matches the actual detection logic and gives clearer guidance.

Suggested change

	echo "clang-format (18/19/20) not found, skipping file formatting. Install with: apt install clang-format-18"
	echo "clang-format not found (tried clang-format-20/19/18 and clang-format), skipping file formatting. Install with: apt install clang-format-18"