Allow outside-module imports in `lazy_loader.attach_stub`

[lagru]

In scikit-image/scikit-image#7007 we have run into https://github.com/scientific-python/lazy_loader/blob/2334bd279d40e0dadd3af48fe4ec494d3ce7f47d/lazy_loader/__init__.py#L204-L206

while trying to apply lazy_loader.attach_stub to skimage.morphology. That submodule tries to import and expose label from skimage.measure again as a public API function. We can workaround this by just making this import one level-deeper in a submodule, e.g. skimage.morphology._util.

However, I was wondering if this limitation is artificial and could be removed or if this constraint prevents other problems for lazy_loader.

[stefanv]

/cc @tlambert03

[tlambert03]

if I recall correctly, that limitation was more like a NotImplementedError...
I do think you'd run into NameErrors if you just naively removed the ValueError, but i think it's something that could be implemented with a little work (need to reorient myself to how that Visitor was working). I'll try to take a look soon

[tlambert03]

ok, now I remember, this "within-module" limitation is actually hardcoded into the attach function itself (not just the stub loader).

https://github.com/scientific-python/lazy_loader/blob/2334bd279d40e0dadd3af48fe4ec494d3ce7f47d/lazy_loader/__init__.py#L71-L77

The lines above limit lazy_loader.attach to modules that are below whatever module attach is being used in. So, if the stub loader is to support super-module imports, the attach function would also need to be updated