Add type overloads to Epochs.average()

[hoechenberger]

This is what I get on main (VS Code, Pylance; latest releases)

This is what I get with this PR

[hoechenberger]

CircleCI complains:

/home/circleci/project/mne/epochs.py:docstring of mne.epochs.BaseEpochs.average:1: WARNING: py:class reference target not found: numpy.float64 [ref.class]

I'm a bit confused, I thought np.float64 was introduces quite a long time ago 🤔

[larsoner]

From dumping the intersphinx registry with

python -m intersphinx_registry.lookup numpy > ~/Desktop/numpy.txt

I checked and it's listed under py:attribute rather than py:class

[hoechenberger]

so it's a bug in the intersphinx file?

[larsoner]

Could be a bug with their doc, or with the type handling in sphinx / autodoc / numpydoc, or could be something that we should add some ignore line for, not sure.