Deferred imports

[dgkuester-nist]

Thanks for the nice library! I have a module that implements a number of dataclasses based on xarray-dataclasses that I wanted to import quickly.

In order to accomplish this, I have a fork that implements lazy loading of numpy and xarray along these lines. To give you a rough sense for the resulting speedup, the initial import time drops from ~320 ms down to ~50 ms on my M2 macbook pro in python 3.9.

Do you think you may be interested in considering integrating this upstream? If so, I'd be happy to open a PR.

[melonora]

@dgkuester Would you be willing to open a PR against the following repo? https://github.com/xarray-contrib/xarray-dataclass

I moved a fork of this repository to the xarray contributors organization which is supported by the xarray team, given that this repository is not maintained. We had people that wanted to move to the use of zarr v3, but couldn't due to xarray dependency constraints here.