add pre-commit, other development setup stuff

[jameslamb]

Based on my experience with #112, this proposes some changes to improve the experience of developing on this repo, and to improve our release confidence in changes.

• adds a pre-commit configuration
• adds a CI job to run pre-commit over all the files
• adds a .gitignore to prevent unwanted files from making it into source control

Notes for Reviewers

Any changes to scripts in the colab/ directory were made automatically like this:

pre-commit run --all-files

I'll propose a follow-up PR after this adding the ruff linter to more thoroughly check the source code. But wanted to do the rest of this first to make the changes easier to review.