`Model.predict_step`.
        *   SavedModel uses its own `Model._saved_model_inputs_spec` attr now
            instead of relying on `Model.inputs` and `Model.input_names`, which
            are no longer set for subclass Models. This attr is set in eager,
            `tf.function`, and graph modes. This gets rid of the need for users
            to manually call `Model._set_inputs` when using Custom Training