MAINT: Use lazy_loader to speed up plopp first import

[MridulS]

In the spirit of scipp/scippneutron#596, this adds lazy_loader to plopp.
Import time goes from

In [1]: %time import plopp
CPU times: user 234 ms, sys: 33.7 ms, total: 268 ms
Wall time: 343 ms

to

In [1]: %time import plopp
CPU times: user 3.52 ms, sys: 3.61 ms, total: 7.12 ms
Wall time: 7.15 ms

(not a very scientific comparison but still seems like a decent speedup).

The attach_stub function works by parsing the .pyi files to infer submodules and functions to expose. It also makes sure that static typecheckers and IDE don't complain too much.

[nvaytet]

Am I right that the backends is now gone from the __all__?
I don't know if it's important or not...

[MridulS]

Hmm, it should be fine I think. As backends is still there explicitly in __init__.py.

It's not in the __all__ list but it is still accesible.

In [1]: import plopp

In [2]: plopp.backends
Out[2]: BackendManager({'2d': 'matplotlib', '3d': 'pythreejs'})

In [3]: 'backends' in plopp.__all__
Out[3]: False

[nvaytet]

What is the reason for renaming the node file to node_class? Was there a clash with something else?

[MridulS]

Yes, helpers.node was clashing with node.py

[nvaytet]

Maybe we should just move the Node and the helpers in a common file? (could be node.py or a differently named file).

[MridulS]

Can we do that in a new PR? I want to make this PR minimal so it's easy to revert in case this messes things up downstream.