xarray/dask read methods

[joshmoore]

On reviewing the most common user-facing API in the wild, @grlee77 pointed to zarr.open as well as the equivalent methods from xarray and dask. With issues like dask/dask#7673 in mind, we may want to have regular tests of these methods.

[grlee77]

That was based on manual inspection of a handful of packages that list Zarr as a dependency, but GitHub-wide searches also indicate these are all widely used:

dask.array's from_zarr
https://github.com/search?q=%22from_zarr%22&type=code
459 source code matches found

xr.open_zarr
https://github.com/search?q=%22from_zarr%22&type=code
1563 source code matches found

zarr.open, zarr.open_array, zarr.open_group
https://github.com/search?q=%22zarr.open%22&type=code
1417 source code matches found