code: def layer_uri(self, layer_name):
          
          for layer in self._vector_layers():
              if layer == layer_name:
                  uri = '{}|layername={}'.format(
                      self.uri.absoluteFilePath(), layer_name)
                  return uri
          else:
              for layer in self._raster_layers():
                  if layer == layer_name:
                      uri = 'GPKG:{}:{}'.format(
                          self.uri.absoluteFilePath(), layer_name)
                      return uri
              else:
                  return None
docs: Get layer URI.
  
          For a vector layer :
          /path/to/the/geopackage.gpkg|layername=my_vector_layer
  
          For a raster :
          GPKG:/path/to/the/geopackage.gpkg:my_raster_layer
  
          :param layer_name: The name of the layer to fetch.
          :type layer_name: str
  
          :return: The URI to the layer.
          :rtype: str
  
          .. versionadded:: 4.0