Update Python version, local currency units

[jdebacker]

This PR updates OG-ZAF so that it is tested on Python 3.12. The symbol for the local currency units in constants.py is also updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.38%. Comparing base (f003a14) to head (7639d93).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
- Coverage   56.43%   55.38%   -1.05%     
==========================================
  Files          12       12              
  Lines         381      381              
==========================================
- Hits          215      211       -4     
- Misses        166      170       +4     

Flag	Coverage Δ
unittests	55.38% <100.00%> (-1.05%)	⬇️

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