feat: add pre-commit configuration

[brucearctor]

Summary

Add a .pre-commit-config.yaml to automate running formatting and linting checks before each commit, and update CONTRIBUTING.md with setup instructions.

Fixes #4946

Changes

.pre-commit-config.yaml (new)

Configures the following hooks:

Hook	Source	Purpose
trailing-whitespace	pre-commit-hooks	Remove trailing whitespace
end-of-file-fixer	pre-commit-hooks	Ensure files end with newline
check-yaml	pre-commit-hooks	Validate YAML syntax
check-added-large-files	pre-commit-hooks	Prevent large file commits
isort	pycqa/isort	Import sorting (uses profile = "google" from pyproject.toml)
pyink	local	Code formatting (uses config from pyproject.toml)
mypy	local	Type checking (runs on src/ only, uses config from pyproject.toml)

Design decisions:

• pyink and mypy are configured as local hooks (using language: system) since they need to use the project's installed versions and configuration. This means contributors must have the dev dependencies installed (uv sync --all-extras or pip install -e ".[dev]").
• pylint is intentionally excluded — it's slow on large codebases and is better suited for CI.
• mypy is scoped to src/ only, matching the existing [tool.mypy] config which excludes tests/ and contributing/samples/.

CONTRIBUTING.md (modified)

Added a new step 5 ("Install pre-commit hooks") to the Development Setup section with instructions for installing and running pre-commit. Subsequent steps are re-numbered.

Testing Plan

To verify locally:

pip install pre-commit
pre-commit install
pre-commit run --all-files

[rohityan]

Hi @brucearctor, Thank you for your contribution! We appreciate you taking the time to submit this pull request. Your PR has been received by the team and is currently under review. We will provide feedback as soon as we have an update to share.

[rohityan]

Hi @xuanyang15 , can you please review this.