ndpyramid validation

[freeman-lab]

From a discussion with @katamartin , we realized it could be very nice to build a tiny utility (possibly in a standalone package) that validates the structure of a zarr ndpyramid from js.

Key things it would do

• try to load the group via zarr-js
• extract pyramid metadata
• extract coordinates and dimensions
• validate everything for internal consistency
• raise any issues

Two key use cases

• short term, via a CLI or tiny standalone web app, let us inspect all dataset properties before trying to incorporate a dataset into an app (this will be especially useful when it comes to coordinates, and just generally helpful for debugging data formatting issues on the js side)
• long term, ideally use the same underlying package to do runtime validation and throw much more helpful error messages when datasets are not formatted correctly

cc @jhamman

[jhamman]

I think this is a great idea. Since we're relying on the array metadata and multiscales spec in consolidated metadata, it may make sense to just write a spec validator for the .zmetadata json. If the spec validates, then a set of functional tests could be run.

FWIW, this would also be a useful test approach in ndpyramid as well. The combination of a validation utility here and a set of unit tests in ndpyramid would be quite a nice combination.