Request: ZARR support

[macromeer]

Hi there,

the cellpose-napari plugin is a great tool for teaching. I was wondering if you could consider implementing ZARR support. After loading a zarr dataset using napari-ome-zarr and setting parameters in the cellpose widget, run segmentation results in the following type error (excerpt):

74 ) -> LayerDataProtocol:
     75     """Multiscale indexing."""
---> 76     return self._data[key]
        self._data = [dask.array<getitem, shape=(236, 275, 271), dtype=uint16, chunksize=(1, 275, 271), chunktype=numpy.ndarray>, dask.array<getitem, shape=(236, 137, 135), dtype=uint16, chunksize=(1, 137, 135), chunktype=numpy.ndarray>, dask.array<getitem, shape=(236, 68, 67), dtype=uint16, chunksize=(1, 68, 67), chunktype=numpy.ndarray>]
        key = (slice(None, None, None), slice(None, None, None), slice(None, None, None), None)
        self = <MultiScaleData at 0x73ce1d598490. 3 levels, 'uint16', shapes: ((236, 275, 271), (236, 137, 135), (236, 68, 67))>

EmitLoopError: 

While emitting signal 'magicgui.widgets.PushButton.changed', an error occurred in a callback:

  TypeError: list indices must be integers or slices, not tuple

Edit: Appears to be an issue with https://github.com/napari/napari/blob/b2f722fd16e08d84cdf5f9af9cbd08b81639bf72/napari/layers/_multiscale_data.py#L71