add lxml typechecking

[jkhsjdhjs]

lxml provides type annotations via the lxml-stubs package. By using this package, we don't need the type: ignore comments when importing lxml anymore. Furthermore, the typehints are adjusted: etree.Element is only a factory function that creates etree._Element instances.

Finally, when generating the docs we introduced a workaround that makes linking to the lxml documentation possible. Since it only replaced lookups for Element with _Element, it isn't necessary anymore and removed.

[s-heppner]

So you're saying that by default, every user of lxml should access the internal class etree._Element?
That seems weird to me.

[jkhsjdhjs]

Every user of lxml is implicitly working with _Element, as Element is just a factory function that returns _Element instances. It's also a bit weird to me, but that's the way it is implemented.

See also: https://stackoverflow.com/questions/76321801/type-hints-for-lxml-etree-element#comment134587997_76321801

[s-heppner]

Okay, then I'm fine that we use etree._Element for the type annotation, as long as we still call etree.Element() to instantiate.