Keep attrs when slicing (feature #908) (#909)

The current `_slice_face_indices` does not copy dataarray attributes to
a sliced grid. This change copies the attrs from the original dataarray
to a sliced grid.

#908

uxarray/grid/slice.py

@@ -125,6 +125,7 @@ def _slice_face_indices(grid, indices, inclusive=True):
                     ds[conn_name].values
                 ),
                 dims=ds[conn_name].dims,
+                attrs=ds[conn_name].attrs,
             )
 
         elif "_connectivity" in conn_name: