Fix Type Annotation in pandas.compat.pickle_compat

[vaibhavhrt]

Part of #25882

Current errors are as follows:

mypy pandas/compat/pickle_compat.py

pandas\compat\pickle_compat.py:141: error: Name 'pkl._Unpickler' is not defined

[vaibhavhrt]

PR coming as soon as figure out how to fix this.

[vaibhavhrt]

Looks like a bug with mypy because _Unpickleris certainly a class in module pickle.
Similar to python/mypy#6383
Only solution I can find is:

class Unpickler(pkl._Unpickler):  # type: ignore

@WillAyd what should I do?

[WillAyd]

I don't think it's a bug - the stdlib just doesn't have annotations for pickle yet and that private class is not exposed in Typeshed. I think ignore is the only option for now

[vaibhavhrt]

Ok, I will open a PR