Fancy reprs for groups and arrays

[d-v-b]

We should have nice reprs for the main Zarr objects, e.g. groups, arrays, stores, etc.

I don't have very specific ideas here, just a bunch of associated thoughts.

• The array, group, and store reprs should all be designed so that people communicating about zarr issues find it natural to re-use these reprs as part of ordinary technical communication.
• For environments where html can be rendered, e.g. jupyter, arrays could have something like dask's array repr. Expressing sharding will be an interesting challenge here.
• For both arrays and groups, the attributes could be rendered under an expandable content element with a fixed-height preview.
• We could ensure that the structured components of array metadata (codecs, etc) also have fancy html reprs, and these could compose in the array repr.
• For groups, it would be nice to display a tree representing all the sub-groups and sub-arrays. But member discovery can be expensive; so we don't want to issue a bunch of (potentially recursive) requests just for the repr. We probably need to have a discussion about caching this kind of thing. With an abstract representation of a group, e.g. the kind proposed in the hierarchy api pr, then a repr can safely display the full known tree.

[sehoffmann]

A very simple and quick remedy until a more comprehensive solution is implemented would be to use output the existing info attribute of groups and arrays. E.g.:

That would already 100x better than the existing behavior: