ENH: Add lazy_loader

[alexrockhill]

A small issue but my import statements get pretty lengthy by importing every function at the top. mne implemented pretty recently lazy_loader so that you can do import dipy and then dipy.align.affine_registration without having to do import dipy.align as well but you don't have the memory hit of having to load all the submodules at initialization. This seems like a nice convenience and it's a small dependency and a couple of lines in each init file (see https://github.com/mne-tools/mne-python/blob/main/mne/decoding/__init__.py for instance). Maybe worth an hour to add this?

[skoudoro]

Hi @alexrockhill,

We are aware of this. See #3056

we just need time and to be careful with this. This is not high priority but it should be done this year.

[alexrockhill]

Sorry only searched issues not PRs, thanks for the info