Can we get a Rzarrlib?

[LTLA]

Just a thought, but would be interesting to think about whether we could have:

• A standalone C/C++ library for zarr.
• Something like Rhdf5lib, but wrapping the above library.

The context is that I can use the standalone library to create tatami_zarr, equivalent to tatami_hdf5. This could then be used to extend the changes in beachmat (see some comments in const-ae/glmGamPoi#52) so that Zarr-based DelayedArrays could be directly translated to C++ representations for native access without going through block processing.

I need to figure out how to do the same thing for TileDB, so that's the general idea for all file-backed DelayedMatrixs.