Update to Python 3.12

[douglatornell]

• Add Python 3.12 to GHA pytest-with-coverage workflow so that we can use the workflow to test whether all the packages moad_tools depends on have been updated to support Python 3.12.
• Add workflow_dispatch trigger to GHA pytest-with-coverage workflow to enable workflow to be triggered from
  GitHub CLI, browser or via API
• Drop Python 3.8, 3.9 & 3.10 from GHA pytest-with-coverage workflow
• Change setup.cfg python_requires to >=3.11
• Change conda environment descriptions to use Python 3.12
  • environment-dev.yaml
  • environment-rtd.yaml
• Change sphinx-linkcheck workflow to Python 3.12
• Change pkg dev doc & README to Python 3.12 for package development

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ff4863c) 56.54% compared to head (b1a10be) 56.36%.

❗ Current head b1a10be differs from pull request most recent head 1f019cb. Consider uploading reports for the commit 1f019cb to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
- Coverage   56.54%   56.36%   -0.19%     
==========================================
  Files          12       12              
  Lines        1107     1107              
==========================================
- Hits          626      624       -2     
- Misses        481      483       +2     

Flag	Coverage Δ
unittests	56.36% <ø> (-0.19%)	⬇️

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