Remove Arrow support from obspec.List

[kylebarron]

Obstore supports returning Arrow RecordBatch from each chunk in obstore.list and returning an Arrow Table from obstore.list_with_delimiter.

I would like this to be an obstore implementation detail instead of a requirement of all obspec implementations.

I had hoped that I would be able to remove the return_arrow keyword from obspec's list methods but still allow obstore's implementation to add the return_arrow keyword as long as it defaults to False and returns a list[ObjectMeta] by default. However it looks like this doesn't pass pylance:

See what I tried in #14

That said, since obspec's list is defined in terms of the Arrow PyCapsule Interface, setting return_arrow=True allows for very generic programming. The return type could be a pandas, Polars, DuckDB, pyarrow, nanoarrow, or arro3 or anything else that supports the protocol. (There is a wrinkle that list requires something that implements the ArrowArray interface, which I'm not sure pandas or polars define, since they only have a concept of a multiple-chunked data structure)