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

flaschengeist/models/__init__.py

@@ -40,6 +40,9 @@ class ModelSerializeMixin:
             return value
         return d
     
+    def __str__(self) -> str:
+        return self.serialize().__str__()
+
 
 class Serial(TypeDecorator):
     """Same as MariaDB Serial used for IDs"""