Add pre-commit including config and GitHub workflow

[josephgruber]

Relevant Issue & Description

https://pythondev.slack.com/archives/C2FMLUBEU/p1757474340679269

This PR introduces pre-commit to automatically enforce code formatting and linting standards across the project, especially related to Ruff.

Pre-commit Setup

• Added .pre-commit-config.yaml with built-in pre-commit hooks including:
  • File validation (large files, merge conflicts, JSON/TOML/YAML syntax)
  • Security checks (private key detection)
  • Code formatting (end-of-file-fixer, trailing-whitespace)
• Added ruff format and lint (check) hooks via the official hook repo

Enforced linting and formatting via GitHub Workflow

• Added a GitHub Actions workflow (.github/workflows/pre-commit.yml) to run pre-commit on all pull requests

Project Configuration Updates

• Updated Python version requirement from >=3.8 to >=3.12 in pyproject.toml
• Added pre-commit>=4.3.0 to lint dependencies
• Updated Ruff version to >=0.13.0
• Updated CONTRIBUTING.md with pre-commit installation and usage instructions

File Formatting

• SVG and CSS files include trailing newlines (per best practices) via the pre-commit hook

Screenshots, if applicable

[josephgruber]

And via the new workflow:

[Quidge]

Some notes but +1 on this add (and how you've added it)!

[Quidge]

I've rolled without using the dedicated pre-commit action before, but something I've added in my own CI is the --show-diff-on-failure flag. It will show a git diff on a failure so you can see the issue in the CI readout. Unsure if the dedicated pre-commit CI action is already doing that under the hood (should be easy enough to check source for that action and confirm if they're using it or not; they likely also have a way to pass arbitrary flags).

[josephgruber]

It does use -show-diff-on-failure: https://github.com/pre-commit/action/blob/main/action.yml#L19

[Quidge]

Isn't exit-non-zero the default? And/or, when pre-commit runs, if a delta is detected, doesn't the delta itself cause pre-commit to trip a failure anyways?

[josephgruber]

Yes. But Ruff can also auto-magically fix some formatting and linting issues. In which case, it exits with a zero status code from what I've seen. We don't have the fix attribute set so it won't auto-fix any issues currently but I'd still suggest we leave this argument on, in case fix is enabled in the future.