This PR sets up zarr-layer so that it correctly gets chunks from pyramids when those pyramid layers don't span the whole globe. I'm working on a system that generates multiscale pyramids like ndpyramid, but it only defines the chunks for tiles which overlap the AOI of the original zarr at each zoom. so while z=0 will always cover the whole globe, some dataset in St Paul will only over (1, 0, 0) at z=1.

This PR is a bit long because it handles several cases:

1. With or without consolidated metadata: without consolidated metadata we use a lazy approach because otherwise it creates too much start up lag.
2. with or without spatial_ref: I would think spatial ref would always be present but we have a fallback case when its not. This is much slower because there are so many network requests to the coordinate arrays.
3. zarr 2 vs 3