Implement chunk write utilities in zarr-array.R

[dblodgett-usgs]

There are a number of unimplemented chunk writing utilities starting here: https://github.com/keller-mark/pizzarr/blob/efe90f760296fedf737d8dd8d12157d8bd579fb9/R/zarr-array.R#L711

[dblodgett-usgs]

This isn't part of any active code -- I'm going to leave till after the initial CRAN release