Refactored the distributed_eval from the contrib package

[cgoina]

@GFleishman, @carsen-stringer , @mrariden The purpose of this PR is to refactor the distributed_eval method so that I can use the code from this package directly in the command line tools package used by Janelia's Nextflow cellpose pipeline, which currently pretty much duplicate this code. The main change was to no longer create the temporary zarr inside the distributed_eval but instead create it in the caller and pass it to the method.