ENH: Get rid of float cast in masked reduction ops

[phofl]

• closes PERF: avoid casting to float in IntegerArray reducing ops #30436 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Shouldn't be user visible

[mroeschke]

IIRC, the nanops functions will still cast the values to float though as they all call?

    if not is_float_dtype(values.dtype):
        ...

[phofl]

Yep, but this might allow optimisations later on. Also, this fixes a couple of mask related bugs in the nan... functions

[mroeschke]

Thanks @phofl