Switch from appdirs to platformdirs

[s-t-e-v-e-n-k]

appdirs has been officially deprecated upstream, the replacement module with more features is platformdirs.

• Closes # (insert issue number)
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Documented in docs/ as appropriate
• Added an entry to the CHANGES file

[codspeed-hq]

CodSpeed Performance Report

Merging #2028 will not alter performance

_{Comparing s-t-e-v-e-n-k:switch-to-platformdirs (74d98a0) with s-t-e-v-e-n-k:switch-to-platformdirs (844bba7)}

Summary

✅ 437 untouched benchmarks