Remove zarr dependency if possible

[jjnesbitt]

Based on this thread, it seems the zarr module might be entirely unnecessary. We should try to remove it and check that zarr checksum outputs remain unchanged.

[yarikoptic]

While removing, for harmonization/centralization of implementation of a walker with dand-cli would be important to implement the same logic of skipping known to be irrelevant to zarr files/folders as done in dandi-cli by exclude_from_zarr to exclude .git etc.