Remove `dirs_exist_ok` argument from `pathlib.Path.copy()`

[barneygale]

(Background: pathlib.Path.copy() is new in Python 3.14, so it hasn't been released yet.)

I don't think there's a compelling case to support a dirs_exist_ok argument in the initial version of Path.copy(). Most Python users don't need "copy and merge directory" functionality. Particularly unlucky users might use the wrong source or target path, and perform a large directory tree merge that is difficult to unpick.

We could add this back in later, in response to user demand.

Linked PRs

• GH-130608: Remove dirs_exist_ok argument from pathlib.Path.copy() #130610