gh-148468: Accept string-like help proxies in argparse

[RaghunandanKumar]

Summary

• restore support for string-like proxy objects in colorized argparse descriptions, epilogs, and argument help text
• normalize formatter text at the string-formatting boundary instead of assuming concrete str objects
• add regression coverage for proxied descriptions, epilogs, and interpolated help text

Issue

• Cannot use lazy translation proxies in argparse help #148468

Testing

• ./python.exe -m test test_argparse
• runtime repro with a minimal LazyStr proxy and parser.format_help()

[savannahostrowski]

Thanks for the PR! As mentioned in my comment on the issue, the str() coercion can go at the re.sub call site rather than at the top of _expand_help. Also, please scope the change down. The _format_action changes and the broader test expansion aren't necessary for this fix.

[bedevere-app]

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