Improved subcommand help text, json error messages, and TimeDelta inputs

[dskrypa]

• Added min/max/int validation options for TimeDelta inputs, similar to NumRange inputs
• Added a wrapper around json.load for Json inputs to provide a more user-friendly error message
• Updated SubCommand so that if no help='...' text is provided as a class kwarg when a sub-Command is defined, but a description or docstring is present, then that description/docstring will be used as the help text when the subcommand choices are displayed in --help text. To prevent that text from being displayed when a description is provided, it is possible to specify help='' with an empty string.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.34%. Comparing base (f0f331e) to head (586da29).
Report is 9 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   98.32%   98.34%   +0.01%     
==========================================
  Files          49       49              
  Lines        6643     6687      +44     
  Branches     1400     1407       +7     
==========================================
+ Hits         6532     6576      +44     
  Misses         95       95              
  Partials       16       16              

Flag	Coverage Δ
unittests	98.34% <100.00%> (+0.01%)	⬆️

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