Create modular packages for zipfile and test_zipfile

[jaraco]

I'm about to embark on once again syncing changes from zipp to zipfile.

Historically, I've manually copied the contents of the cpython branch to the relevant files in this repository, but that process is error prone (because it involves syncing a whole file to a portion of another file).

I'd like to instead create packages for zipfile and test_zipfile, such that the functionality that's synced with zipp can be kept separate from other zipfile functionality. Moreover, late versions of zipp bring in extra dependencies so a package can also serve as a home to vendor such functionality.

I'm not suggesting to change the user's signature at all. The names will still be presented through the zipfile module unchanged.

Linked PRs

• gh-98098: Create packages from zipfile and test_zipfile #98103

[jaraco]

I tried moving most of zipfile.py to zipfile/_core.py but that caused problems with all of the global constants in that file, many of which are treated as mutable (at least for tests).

[hauntsaninja]

Looks like this can be closed, but not touching it since I see it was assigned to Yhg1s and I don't know what that means