Add unsafe readChunkDirect and writeChunkDirect to Arrays

[normanrz]

For some applications, it is useful to supply the already encoded chunks to be written into a Zarr array without decoding+encoding. An example is a JPEG -> zarr (with jpeg codec), where is would result in loss of quality if the data had to be decoded and encoded. So, there should be functions on the Array classes to read and write chunks directly. This should also work with sharding, where a user would supply multiple chunks that go into a shard.

[konstibob]

If I am understanding you correctly, the idea is to let people hand Zarr chunks that are already in the right, compressed form and have them stored without Zarr unpacking them and re-packing them.

This only makes sense when someone supplies a whole chunk. If a write only covers part of a chunk, we can't avoid the round-trip to change part of compressed data. You have to unpack it, edit it, and repack it, which means that piece does lose a little quality.

But we are saving compute time / data quality in case the whole chunk is edited and not only parts of it.