TYP: overload maybe_downcast_numeric and maybe_downcast_to_dtype

[iasoon]

xref #37715

Overload type definitions for these methods so that passing in an ndarray returns an ndarray.
This allows removing two more ignored mypy errors.

[rhshadrach]

Instead of using overloads, does it make sense to have an ArrayLikeT, i.e. a TypeVar bound to np.ndarray | ExtensionArray?

cc @simonjayhawkins @Dr-Irv

[Dr-Irv]

Instead of using overloads, does it make sense to have an ArrayLikeT, i.e. a TypeVar bound to np.ndarray | ExtensionArray?

cc @simonjayhawkins @Dr-Irv

I think (but I'm not sure) that the times to use a TypeVar are when subclassing gets involved with respect to self . I think the overload approach is correct here, but also agree with @twoertwein that with ArrayLike including np.ndarray, it's better to have one overload for np.ndarray and a different one for ExtensionArray

[iasoon]

Thanks for the comments!
I played around a bit with the typevar route, but I do not think it is sound in this case: both methods will return np.ndarray when passed np.ndarray, but could return either ExtensionArray or np.ndarray when passed ExtensionArray.
I agree non-overlapping overloads are cleaner here, I resolved that.

[twoertwein]

Thank you @iasoon!