gh-141388: Fully support non-function callables as annotate functions

[dr-carlos]

• Any callable can be used as an __annotate__ function in 3.14, but annotationlib will start throwing errors if the format is not implemented.
• This is an initial implementation to support them as first-class citizens included here, mostly in call_annotate_function()
• Currently this implementation supports: methods, class/static methods, class instances that are callable, classes and generics themselves, partial, wrapped, singledispatch, and cached functions. 'Builtin' (C) callables can't really be supported because they have no __code__, __globals__, etc., so a ForwardRef or stringification using the current techniques is impossible. Let me know if there are any more callables to implement, some more special-casing will probably be required.
• Initial tests are present but not thorough. It should work for all parts of annotationlib, but tests are mostly present on call_annotate_function() for now.
• Opening a PR now to seek feedback on the implementation and decide on whether the extra complexity is worth it. If there is interest, I'll add more thorough tests, etc.

• Issue: __annotate__ Functions don't actually need to be functions #141388