One time ABI breakage

Abstract I’d like to propose that we have a one time break in the stable ABI, such that extensions can be compiled into one of two builds: Support versions up to 3.15 Support version 3.12 (3.14 for 32 bit builds) and later. With this break, it will not be possible to compile a single binary that supports both 3.11 and 3.16, or both 3.13 and 3.16 for 32 bit builds. Having this break will allow significant improvements in maintainability and performance of CPython. Motivation Maintainabili...