Add ruff linting

[alongd]

Add ruff as ARC's linter: config in pyproject.toml, workflow in .github/workflows/ruff.yml, status badge in the README.

Ruff currently runs in non-blocking mode (continue-on-error: true)

[Copilot]

Pull request overview

Adds Ruff as a (currently non-blocking) linter/formatter check for ARC, wiring it into repo config, CI, and documentation so contributors can see lint status on PRs.

Changes:

• Add Ruff configuration to pyproject.toml (rule selection, ignores, per-file ignores, and format settings).
• Add a GitHub Actions workflow to run ruff check and ruff format --check on PRs and main (non-blocking).
• Add a Ruff status badge to the README.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
README.md	Adds a Ruff workflow badge to surface lint status.
pyproject.toml	Introduces Ruff lint/format configuration and project-specific excludes/ignores.
.github/workflows/ruff.yml	Adds a CI workflow that runs Ruff in continue-on-error mode.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.13%. Comparing base (606bbe2) to head (f7bd0ab).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #860      +/-   ##
==========================================
- Coverage   60.13%   60.13%   -0.01%     
==========================================
  Files         102      102              
  Lines       31043    31043              
  Branches     8082     8082              
==========================================
- Hits        18669    18667       -2     
  Misses      10067    10067              
- Partials     2307     2309       +2     

Flag	Coverage Δ
functionaltests	60.13% <ø> (-0.01%)	⬇️
unittests	60.13% <ø> (-0.01%)	⬇️

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[alongd]

@calvinp0, as discusses offline, now we ignore the entire molecule module