Moved decorators._set_parser_prog() to argparse_custom.set_parser_prog().

[kmvanbrunt]

set_parser_prog() is a good utility method so I made it a public part of the argparse_custom module.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.41%. Comparing base (dd46c35) to head (1261cb0).
⚠️ Report is 106 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1466      +/-   ##
==========================================
- Coverage   98.41%   98.41%   -0.01%     
==========================================
  Files          21       21              
  Lines        5865     5864       -1     
==========================================
- Hits         5772     5771       -1     
  Misses         93       93              

Flag	Coverage Δ
unittests	98.41% <100.00%> (-0.01%)	⬇️

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