Fix an error in unmarshalRecordRecursively

A refactor left a spurious array slicing.

schema/tuples.go

@@ -88,7 +88,7 @@ func unmarshalRecordRecursively(record []byte) (map[string]any, error) {
 		s = strings.TrimPrefix(s, "@cee:")
 		if strings.HasPrefix(s, "{") {
 			var m2 map[string]any
-			if err := json.Unmarshal([]byte(s[5:]), &m2); err == nil {
+			if err := json.NewDecoder(strings.NewReader(s)).Decode(&m2); err == nil {
 				m["message"] = m2
 			}
 		}