Is your feature request related to a problem? Please describe.
Currentlyjson_serializer is based on a hidden class _JsonSerializer (same for json_deserialize) and that doesn't allow the users to define their own custom json serde via extending json.JSONEncoder and json.JSONDecoder. For certain applications that the json request has many fields of various types using the current implementation makes the request handling very manual in transform_fn which is not scalable.