General refactor/restructure of project

[klaasnicolaas]

General restructure/refactor of the project.

• Updates all sub-dependencies
• Replace flake + all plugins + isort + pyupgrade + bandit by ruff
• Address all issues raised by ruff
• Simplify GitHub actions runs, to have a little fewer jobs/faster runtimes and leverage caching capabilities of other actions
• Remove old configs no longer in use
• Move examples to new folder

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (a4c463b) 100.00% compared to head (20faa68) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #141   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines           84        90    +6     
  Branches         9         9           
=========================================
+ Hits            84        90    +6     

Impacted Files	Coverage Δ
namur/models.py	100.00% <100.00%> (ø)
namur/namur.py	100.00% <100.00%> (ø)

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