[models] Add __str__ function for all serialized models (for debug)

flaschengeist/models/__init__.py

@@ -39,6 +39,9 @@ class ModelSerializeMixin:
             key, value = d.popitem()
             return value
         return d
+    
+    def __str__(self) -> str:
+        return self.serialize().__str__()
 
 
 class Serial(TypeDecorator):