Implement array get methods.

[dblodgett-usgs]

There are quite a few TODOs starting here for get methods of the array class.

https://github.com/keller-mark/pizzarr/blob/efe90f760296fedf737d8dd8d12157d8bd579fb9/R/zarr-array.R#L978

[dblodgett-usgs]

Should these be in our initial CRAN release @keller-mark ?

[dblodgett-usgs]

The issue is mostly done but not fully complete. The core get methods all work — get_item, get_basic_selection, get_basic_selection_zd, get_basic_selection_nd, get_orthogonal_selection, and get_selection are all implemented and tested.

Still unimplemented (stubs with TODO):

get_coordinate_selection — point/vectorized indexing
get_mask_selection — boolean mask indexing
chunk_getitems — batch chunk retrieval
chunk_buffer_to_raw_array — unused stub