Add types for xmldiff

[kasium]

No description provided.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[kasium]

Fails with stub_uploader.metadata.InvalidRequires: Expected dependency lxml-stubs to be present in the stub_uploader allowlist. Can someone please support

[srittau]

It seems that the lxml project instead recommends to use types-lxml instead: That said, I'm a bit wary to officially depend on a non-typeshed project that uses the types- prefix, which we unfortunately couldn't reserve as PyPI still doesn't support namespaces (pypi/warehouse#4967, pypi/warehouse#4164, pypi/warehouse#2589).

[kasium]

Okay, but should I use then? If I don't add any subs it fails too :)

[srittau]

One option is to just alias it for now:

ET: TypeAlias = Any  # lxml.etree._ElementTree

This is the version I'm most comfortable with, considering that types-lxml is not a name I want to support, and lxml-stubs is outdated.