Writes model weight histograms to Tensorboard.

def _write_weight_histograms(self, iteration:int)->None:
        "Writes model weight histograms to Tensorboard."
        generator, critic = self.learn.gan_trainer.generator, self.learn.gan_trainer.critic
        self.hist_writer.write(model=generator, iteration=iteration, tbwriter=self.tbwriter, name='generator')
        self.hist_writer.write(model=critic,    iteration=iteration, tbwriter=self.tbwriter, name='critic')