Allow setting of write_empty_chunks for zarr.core.Array objects

[RKuttruff]

When opening a Zarr group via zarr.hierarchy.open_group() there is currently no way to specify write_empty_chunks=False, this can be problematic when appending to existing zarr groups with sparse data as found in pydata/xarray#8009 / pydata/xarray#8016. A simple solution to this would be setting write_empty_chunks=False for Array objects as they are retrieved from the group. Or, perhaps, allowing the user to specify their preference for write_empty_chunks for Arrays in the group when opening/getting the individual Arrays from the group.

[joshmoore]

cc: @jni

[d-v-b]

Thanks @RKuttruff, I have felt this problem acutely.

One fundamental challenge for zarr-python is the friction between a) dynamic options for accessing arrays (like read_only, and write_empty_chunks, among others) and b) the MutableMapping API used by zarr groups to represent their contents. As long as we support array = group['my_array'], it's hard to figure out where a user can provide the dynamic options.

As a stopgap, we should make these dynamic options correspond to set-able properties of arrays, so users can modify the arrays after getting them from the group. I find this really distasteful, but it should work.

[jhamman]

I see there being two options for making this work given the current API.

First, lean into using the state of the Array via setters:

array = group['my_array']
array.write_empty_chunks = False
array[:] = ...

Second, utilize some sort of scoped config:

with zarr.config.set(write_empty_chunks=False):
    array = group['my_array']
    array[:] = ...

Neither are perfect but I think I would lean toward the latter option if I had to.

[jhamman]

We're sorting this out for 3.0 over in #2409. I'm going to close this in favor of the more recent ticket.