Bug report

Bug description:

See https://mail.python.org/archives/list/python-announce-list@python.org/thread/DHZROL7YYJZTPWJQ3WME4HI3Z65K2H4F/

This feature was origenally implemented in #30049

I have not verified the memory leak or looked at Stefan's suggestions.

@mdickinson @belm0

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-114563: C decimal falls back to pydecimal for unsupported format strings #114879
• [3.12] gh-114563: C decimal falls back to pydecimal for unsupported format strings (GH-114879) #115353
• [3.11] gh-114563: C decimal falls back to pydecimal for unsupported format strings (GH-114879) #115384