Spec version vs `zarr_format`

[d-v-b]

The zarr_format metadata is an integer, but the spec document uses a string identifier that can represent major and minor versions. So, unlike the spec document, the zarr_format metadata cannot ever represent a minor version. Is this a problem? It seems like skew between the spec version and zarr_format is a recipe for trouble, but I don't see how to fix this without some disruption.

cc @WardF, as this relates to some of our conversations from the community meeting the other day, and I think the netcdf perspective would be useful here.