Add Ruff and pre-commit checks

[genedan]

Summary of Changes

Adds Ruff and pre-commit to workflows.

Related GitHub Issue(s)

#651

Additional Context for Reviewers

Try out pre-commit and let me know what you think. Already, I'm seeing that it's a little annoying if you want to push small changes that you know will pass - for example, I removed some verbose comments that Claude left behind, but all the checks ran again prior to push, taking an extra 4 minutes for a very trivial change.

Checklist

• I passed tests locally for both code (uv run pytest) and documentation changes (uv run --directory docs jb build . --builder=custom --custom-builder=doctest)

---

Note

Low Risk
Tooling and lint configuration only; no runtime library behavior changes beyond removing unused test imports.

Overview
Introduces Ruff (Pyflakes/pycodestyle subset E4/E7/E9/F) as required CI and optional local gates, without forcing a repo-wide cleanup in one shot.

CI: A new Ruff workflow runs on pushes and PRs, linting only changed *.py files. It runs ruff check with per-file-ignores cleared (lint.per-file-ignores={}), so edited files must meet the full rule set even though pyproject.toml still lists grandfathered ignores for untouched legacy files.

Local: pre-commit installs pre-commit and pre-push hooks: Ruff on push (same empty per-file-ignores override) and full uv run pytest on every push.

Config: ruff and pre-commit are added to the dev optional dependencies; uv.lock is updated accordingly. One test file drops unused imports after lint touched it.

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[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 14.9% of exported symbols fully typed (197 / 1323)

	Known	Ambiguous	Unknown	Total
Project (head)	197	111	1015	1323

Other symbols referenced but not exported by chainladder: 13

	Known	Ambiguous	Unknown	Total
Other (head)	3	1	9	13

Symbols without documentation:

• Functions without docstring: 316
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): no exported symbol type-completeness changes detected.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.53%. Comparing base (8209f46) to head (f40ee9d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1198      +/-   ##
==========================================
+ Coverage   91.25%   91.53%   +0.28%     
==========================================
  Files          91       91              
  Lines        5395     5575     +180     
  Branches      688      717      +29     
==========================================
+ Hits         4923     5103     +180     
  Misses        338      338              
  Partials      134      134              

Flag	Coverage Δ
unittests	91.53% <ø> (+0.28%)	⬆️

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[genedan]

Good news - you can simply uncheck "Run Git hooks" when making a tiny non-breaking change to bypass running the whole suite locally.

For example, say you're working on an issue and get 99% of the work done. You run the pre-commit checks by default. But then you've got some minor edits (like removing a comment), which you can push immediately by unchecking "Run Git hooks" or whatever your IDE equivalent is.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

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^{Reviewed by Cursor Bugbot for commit 8e94531. Configure here.}

[genedan]

Running uv run ruff check by itself will yield a large number of errors ~200, scattered throughout the repository. To not clog up this PR, I've set the workflow to only check modified files. After this PR gets merged in, we can fix the files a handful at a time, and once the repo is clean, we can add back in the checks on the whole project.

[henrydingliu]

Good news - you can simply uncheck "Run Git hooks" when making a tiny non-breaking change to bypass running the whole suite locally.

For example, say you're working on an issue and get 99% of the work done. You run the pre-commit checks by default. But then you've got some minor edits (like removing a comment), which you can push immediately by unchecking "Run Git hooks" or whatever your IDE equivalent is.

where is this checkbox? can you attach a screenshot