Replace isort, flake8, and pyupgrade with ruff

[tpvasconcelos]

See: https://github.com/charliermarsh/ruff

Applied as many rules as possible from https://beta.ruff.rs/docs/rules/#ruff-specific-rules-ruf but left a few comments out for now as it would be too much work to refactor every single flagged case.

solves #115

[codecov-commenter]

Codecov Report

Patch coverage: 82.60% and project coverage change: +18.31% 🎉

Comparison is base (a3e8193) 68.12% compared to head (ee627bc) 86.43%.
Report is 1 commits behind head on main.

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Additional details and impacted files

@@             Coverage Diff             @@
##             main     #131       +/-   ##
===========================================
+ Coverage   68.12%   86.43%   +18.31%     
===========================================
  Files          11       10        -1     
  Lines         389      376       -13     
  Branches       66       66               
===========================================
+ Hits          265      325       +60     
+ Misses        115       39       -76     
- Partials        9       12        +3     

Flag	Coverage Δ
unittests	86.43% <82.60%> (+18.31%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/ridgeplot/_utils.py	97.72% <ø> (-0.06%)	⬇️
src/ridgeplot/_ridgeplot.py	57.14% <57.14%> (+25.56%)	⬆️
src/ridgeplot/_figure_factory.py	81.25% <80.00%> (+48.43%)	⬆️
src/ridgeplot/_colors.py	96.55% <100.00%> (-0.06%)	⬇️
src/ridgeplot/_kde.py	74.07% <100.00%> (-0.93%)	⬇️
src/ridgeplot/_testing.py	100.00% <100.00%> (ø)
src/ridgeplot/_types.py	100.00% <100.00%> (ø)
src/ridgeplot/datasets/__init__.py	86.66% <100.00%> (-1.57%)	⬇️

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