Writes a single scalar value for a gradient statistic to Tensorboard.

def _add_gradient_scalar(self, name:str, scalar_value)->None:
        "Writes a single scalar value for a gradient statistic to Tensorboard."
        tag = self.name + '/gradients/' + name
        self.tbwriter.add_scalar(tag=tag, scalar_value=scalar_value, global_step=self.iteration)