[keras] adds write_summary

writes keras model summary to law target

keras.py

@@ -1330,3 +1330,11 @@ class GroupedXEnt(tf.keras.losses.Loss):
             class_weight=self.class_weight,
             epsilon=self.epsilon,
         )
+
+
+def write_summary(model, target):
+    """write tf keras model summary to law target"""
+    summary = []
+    model.summary(print_fn=lambda x: summary.append(x))
+    summary = "\n".join(summary)
+    target.dump(summary)