[v3] Groups and Arrays do not implement `__enter__` / `__exit__` protocols

[jhamman]

In Zarr-Python 2, Groups and Arrays implemented __enter__ and __exit__ so that they could be used in a context manager and the underlying store would be automatically closed. We have not implemented this in Zarr-Python 3 yet though I can't think of a specific reason as to why we couldn't.

This issue tracks the development of this feature in Zarr-Python 3.

[dikwickley]

@jhamman I added a draft PR that can add these methods.

I found the older implementation here for groups

but couldn't find for arrays.

are there any other cases I need to handle?

[TomaSusi]

This would be really great to have!