TYP: Annotations in pandas/core/nanops.py
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

In the CI logs:
```
>           from scipy.stats import kendalltau, spearmanr
E           ModuleNotFoundError: No module named 'scipy'
```

For this to work you need to first do `from scipy import stats`, then do the specific imports.  I think a recent change in the test imports may be the reason why this PR was affected, but the import here definitely needs to be updated. apparently a test in test_nanops is missing a td.skip_if_no_scipy.  have you rebased recently? > have you rebased recently?

Yes, I have

 looks ok, @MomIsBestFriend there is the return type of nanprod that is incorrect (and not erroring) ?
 > looks ok, @MomIsBestFriend there is the return type of nanprod that is incorrect (and not erroring) ?

On my PC the type is

```python
<class 'numpy.float64'>
```

I think that's is because my CPU is 64-bit architecture, should I annotate it as
```python
Union[np.float32, np.float64]
```
to add support for 32-bit architecture CPUs as well?
or just to annotate it as ```float``` or ```np.float```?


cc @jreback @simonjayhawkins  > or just to annotate it as `float` or `np.float`?

just `float` for now, since np.float resolves to `Any` without stubs for numpy. > pls rebase as well

Rebased. lgtm. @simonjayhawkins or @WillAyd if any comments. let's merge if good rather than add things to this one. ideally we keep basic typing PRs non-controversial and separate out the controversial to other PRs. Thanks @MomIsBestFriend 