use /paths/~1untyped/post request_body: DataclassCodec
untyped-server-decode: native Untyped(inner=Inner(v=1), seq=[1, 2]) json={"inner":{"v":1},"seq":[1,2]}
untyped-server-decode-scalars: native Untyped(inner=Inner(v=None), seq=5) json={"inner":{},"seq":5}
