BUG: rechunk roi data after slicing

So the roi image, when used later either in another view call or saving
with to_ngff_zarr, we do not run into the error:

```
ValueError: Attempt to save array to zarr with irregular chunking, please call `arr.rechunk(...)` first
```

Author: thewtex

itkwidgets/viewer.py

@@ -429,6 +429,7 @@ async def get_roi_image(self, scale: int = -1, name: str = 'Image') -> NgffImage
             multiscales = from_ngff_zarr(store)
             loaded_image = multiscales.images[scale]
             roi_data = loaded_image.data[roi_slices]
+            roi_data = roi_data.rechunk(loaded_image.data.chunksize)
             return to_ngff_image(
                 roi_data,
                 dims=loaded_image.dims,