docs: def _advance_window(self):
          """Update values in current window and the current window means and variances."""
          x_to_remove, y_to_remove = self._x_in_window[0], self._y_in_window[0]
  
          self._window_bound_lower += 1
          self._update_values_in_window()
          x_to_add, y_to_add = self._x_in_window[-1], self._y_in_window[-1]
  
          self._remove_observation(x_to_remove, y_to_remove)
          self._add_observation(x_to_add, y_to_add)