xarray integration tests

[rwegener2]

What has been built?

This PR adds an integration test to test reading and writing xarray data in zarr. Works toward #2185

How was it done?

A new file test_xarray.py was added that includes

1. A fixture which generates an xarray object
2. A test which tests 4 common compressors on v2 zarr

A new environment called downstream was added in the pyproject.toml.

How can it be tested?

hatch -e downstream run run

or:
hatch -e downstream shell
pytest -k xarray

Notes

This PR is still a draft. Todos before merging:

• parameterize the dataset() fixture for multiple datatypes and array sizes
• parameterize the store() fixture for multiple store types
• parameterize the test_roundtrip_v2() for multiple chunk sizes
• use pytest importorskip as needed (for xarray)

We are still unclear on how v3 will allow the user to set compression used by xarray.Dataset.to_zarr, so we have used the v2 standard. Pending changes on communication between xarray and zarr about compression alluded to by @jhamman.

[joshmoore]

Thanks, @rwegener2! I've launched the workflows.