Repo-wide ruff pass + enforce it in CI

[asmacdo]

mechababs has no [tool.ruff] config and no CI workflows, so formatting is unenforced and drifting. ruff format --check currently reports 17 files would be reformatted, 3 already formatted. (ruff check . passes clean — this is purely formatting.)

Now that the repo takes outside contributions, unenforced formatting is a contributor-facing papercut rather than just an internal one: a PR gets reformatted incidentally, or a reviewer spends the round-trip on it.

Do it as one deliberate pass

Not piecemeal. Running ruff format on individual files as you touch them rewrites unrelated lines into an otherwise small diff — that has already happened once here, where a test-file rename commit also carried a wholesale reformat of that file, making the rename unreviewable.

Scope

• Add [tool.ruff] to pyproject.toml.
• One repo-wide ruff format commit, separate from any behaviour change.
• Add a CI workflow running both steps, matching what babs runs: ruff check . and ruff format --check .. These are two separate steps; ruff check alone does not catch formatting.

Pin the ruff version in CI rather than pip install ruff — an unpinned install silently changes the rule set on someone else's PR (this bit babs: PennLINC/babs#397).

[asmacdo]

This will be our first gh action on this repo.