Bump minimum Python supported to 3.9, fix test clean up

[tekktrik]

• Fix path separators for Windows in Makefile
• Drop ongoing support for CPython3.8
• Use chmod to change perrmissions of files before deleting
• Update typing for Python 3.9
• Update requirements
• Update sphinx config file
• Update pre-commit hooks
• FIx issue with combining lists

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (9379a66) to head (987606e).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #84   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           32        32           
  Lines         1356      1352    -4     
=========================================
- Hits          1356      1352    -4     

Flag	Coverage Δ
macos-latest-py-3.8	?
macos-latest-py-3.9	100.00% <100.00%> (?)
ubuntu-latest-py-3.10	100.00% <100.00%> (ø)
ubuntu-latest-py-3.11	100.00% <100.00%> (ø)
ubuntu-latest-py-3.12	100.00% <100.00%> (ø)
ubuntu-latest-py-3.13	100.00% <100.00%> (?)
ubuntu-latest-py-3.8	?
ubuntu-latest-py-3.9	100.00% <100.00%> (ø)
windows-latest-py-3.8	?
windows-latest-py-3.9	100.00% <100.00%> (?)

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