Revert to zarr v2 #144
Description
Moving to Zarr v3 in tsinfer is too difficult to do quickly, so revert to Zarr v2 here while that change is being made so that we can make releases.
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Moving to Zarr v3 in tsinfer is too difficult to do quickly, so revert to Zarr v2 here while that change is being made so that we can make releases.