Add darker pre-commit hook

[kelle]

I think both David and I have been using ruff. We could document that as our preference and add it as a pre-commit hook.

[kelle]

I think we should use BOTH Black and Ruff. Black for formatting and Ruff for "fixes". Something like this:
astral-sh/ruff-vscode#126

I think I want Black to autoformat but maybe I just want Ruff to tell me things and NOT autoformat.

[kelle]

Maybe we want to go ahead and add the Black auto hook thing. I think it's better to do sooner rather than later.

[dr-rodriguez]

I would recommend instead of a Black pre-commit hook to instead use darker. Darker applies the same styling as Black but only on lines changed in a commit. So instead of changing the full file it only changes a few lines.

Example .pre-commit-config.yaml file:

# See https://pre-commit.com for more information
# See https://pre-commit.com/hooks.html for more hooks
# To install:
# pip install pre-commit
# pre-commit install --allow-missing-config
repos:
- repo: https://github.com/akaihola/darker
  rev: 1.7.2
  hooks:
    - id: darker