Support zarr formats natively

[keller-mark]

We need zarr support in R to be able to write expression matrices, and potentially to write hdf5 or other objects directly to zarr representations (like AnnData.write_zarr) See https://github.com/gdkrmr/zarr-R

There is also a lot of interest in other places zarr-developers/community#18 https://spacetx-starfish.readthedocs.io/en/stable/help_and_reference/working_with_starfish_outputs/IntensityTable/#serialization

[wolfganghuber]

There is now the Rarr package by Mike Smith: https://github.com/grimbough/Rarr
It's been submitted to Bioconductor and should pop up there sooner or later.