Special formatting of ranges as choices instead of listing entries

[jonrebm]

We're using an argument with choices=range(0, 256). This leads to a long list of all the options in the generated documentation. This patch reduces code duplication by moving choice formatting to a separate function invoked for action groups, positional arguments, and optional arguments. The only functional change is that for objects of type range with a step of one, formatting is changed from "Possible choices: 0, 1, 2 [...]" to "Value range: 0 to 256"

[codecov[bot]]

Codecov Report

:x: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review. :warning: Please upload report for BASE (main@2a2a202). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
sphinxarg/ext.py	42.85%	3 Missing and 1 partial :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #69   +/-   ##
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  Coverage        ?   46.97%           
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  Files           ?       12           
  Lines           ?      960           
  Branches        ?      205           
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  Hits            ?      451           
  Misses          ?      468           
  Partials        ?       41           

Flag	Coverage Δ
unittests	46.97% <42.85%> (?)

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