Pre commit conf

[g-as]

Description

Following #877, I added a .pre-commit-config.yaml conf file & ran trivial lints (trailing whitespace + EOF fixers)

See https://pre-commit.ci/ to automate integration.

The feature or problem addressed by this PR

What your changes do and why you chose this solution

Checklist

• [x] Checked that no other issues or pull requests exist for the same issue/change
• [ ] Added tests covering the new functionality
• [ ] Updated documentation OR the change is too minor to be documented
• [ ] Updated CHANGELOG.md OR changes are insignificant