Show the `xs` (inputs) and `ys` (targets) on a figure of `figsize`.

def show_xys(self, xs, ys, imgsize:int=4, figsize:Optional[Tuple[int,int]]=None, **kwargs):
        "Show the `xs` (inputs) and `ys` (targets) on a figure of `figsize`."
        rows = int(np.ceil(math.sqrt(len(xs))))
        axs = subplots(rows, rows, imgsize=imgsize, figsize=figsize)
        for x,y,ax in zip(xs, ys, axs.flatten()): x.show(ax=ax, y=y, **kwargs)
        for ax in axs.flatten()[len(xs):]: ax.axis('off')
        plt.tight_layout()