code: def new_grid_stack_with_pix_grid_added(self, pix_grid, regular_to_nearest_pix):
          
          pix = PixGrid(arr=pix_grid, regular_to_nearest_pix=regular_to_nearest_pix)
          return GridStack(regular=self.regular, sub=self.sub, blurring=self.blurring, pix=pix)
docs: Setup a grid-stack of grid_stack using an existing grid-stack.
          
          The new grid-stack has the same grid_stack (regular, sub, blurring, etc.) as before, but adds a pix-grid as a \
          new attribute.
  
          Parameters
          -----------
          pix_grid : ndarray
              The grid of (y,x) arc-second coordinates of every image-plane pixelization grid used for adaptive \
               pixelizations.
          regular_to_nearest_pix : ndarray
              A 1D array that maps every regular-grid pixel to its nearest pix-grid pixel.