ENH: add np.nan* funcs to cython_table
- [x] closes #19629
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

This PR ensures that ``Series.agg`` can correctly take np.nan* funcs as inputs, e.g.:

```python
>>> pd.Series([1,2,3,4]).agg(np.nansum)
10
```

Previously that operation returned a Series. See #19629 for details.

Tests are added through the use of ``_get_cython_table_params`` in the parametrisation of ``test_agg_cython_table`` test function in ``series/test_apply``/``frame/test_apply``.