import torchgeo.datasets is slow

[calebrob6]

Description

python -X importtime -c "import torchgeo.datasets" takes 29 seconds for me. We may want to switch to a dynamic/lazy import pattern. Happy to implement this if we can agree on a pattern!

Steps to reproduce

see above

Version

latest

[adamjstewart]

> time python3 -c 'import torchgeo.datasets'

________________________________________________________
Executed in    1.76 secs    fish           external
   usr time    1.47 secs    0.10 millis    1.47 secs
   sys time    0.28 secs    2.10 millis    0.28 secs

Not great, but much faster than 29 sec. Roughly 3/4 of that time is taken up by import torch. I don't think lazy imports are possible in that case, since we need torch.utils.data.Dataset at a bare minimum.

[calebrob6]

If I do that, then I get numbers ~7 seconds