For unions, handle string types last

[brentyi]

Examples:

• For arg: Optional[str] and arg: str | None, --arg None will create a None object instead of a string.
  • This was already happening.
• For arg: str | bool, --arg True will create a boolean instead of a string.
  • This is new.
• For arg: str | int, integers will be created when possible instead of strings.
  • This is new.

Questions raised:

• Should we also handle arg: tuple[str, ...] | int?
• How about Optional[list[str]]?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.78%. Comparing base (af0ae1e) to head (37dc485).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #209   +/-   ##
=======================================
  Coverage   99.78%   99.78%           
=======================================
  Files          28       28           
  Lines        2302     2302           
=======================================
  Hits         2297     2297           
  Misses          5        5           

Flag	Coverage Δ
unittests	99.78% <100.00%> (ø)

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