refactor: split metadata into v2 and v3 modules#2163

d-v-b merged 8 commits intozarr-developers:v3zarr-developers/zarr-python:v3from

d-v-b:refactor/metadata-by-zarr-versiond-v-b/zarr-python:refactor/metadata-by-zarr-versionCopy head branch name to clipboard