Refactor argparse custom

[kmvanbrunt]

• Require devs to use Cmd2ArgumentParser-based parsers.
• Moved previously-patched functions into Cmd2ArgumentParser.
• Simplified creation of cmd2-specific argparse.Action attributes.
• Made common prefix for all private cmd2 attributes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.57%. Comparing base (b726c52) to head (95be12b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1621      +/-   ##
==========================================
+ Coverage   99.51%   99.57%   +0.05%     
==========================================
  Files          21       21              
  Lines        4766     4715      -51     
==========================================
- Hits         4743     4695      -48     
+ Misses         23       20       -3     

Flag	Coverage Δ
unittests	99.57% <100.00%> (+0.05%)	⬆️

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[tleonhardt]

LGTM