zarr support?

[ivirshup]

Likely of interest to @rcannood.

If R starts to get good support for zarr (zarr-developers/community#18), would support for reading the AnnData's written to zarr be in scope here? Particularly for a native reader/ writer as in #46 #48?

The hdf5 files are great for portability, but it's quite nice to have easier access to contemporary compression algorithms and access over http. But, it is an extra thing to maintain.

[lazappi]

I don't really know anything about zarr but I would say this is probably possible if there is some core R/Bioconductor package for handling the low-level stuff. Probably also depends on how much effort it takes to setup/maintain and if the format starts being used in practice.

For now I think we probably just leave this issue open as a reminder to keep an eye on it.