In Python 3.12, when multiple arguments are given to PurePath(), the initialiser calls os.path.join() to join them. This is reasonably slow. For Python 3.13 we can make it faster by:

1. Deferring joining of arguments until strictly needed
2. (Maybe) re-implementing os.path.join(), as pathlib did before gh-94909: fix joining of absolute and relative Windows paths in pathlib  #95450.

Linked PRs

• GH-104996: Defer joining of pathlib.PurePath() arguments. #104999
• [3.12] GH-104996: Defer joining of pathlib.PurePath() arguments. (GH-104999) #105483
• GH-104996: Implement path joining algorithm in pathlib #105484