[Bug] Code Generation Attempt Unintendedly Triggered

Given the abstract class (as well as a mixin version of the code) any sub-classes seem to trigger code generation attempts. However, I'm creating a wrapper class that consumes Built generated classes. This seems like buggy behavior. Either that, or it highlights the need for some kind of `@built_ignore()` annotation.

``` dart
abstract class BuiltJsonSerializable,
V extends Builder> {
Serializer get serializer;

Map toJsonMap() => jsonDecode(toJsonString());

String toJsonString() => standardSerializers.toJson(serializer, toModel());

T? toModel();

T? modelFromJsonString(String serialized) {
try {
T? model = standardSerializers.fromJson(serializer, serialized);
return model;
} on DeserializationError catch (e) {
Get.log('[${T.toString()} DESERIALIZATION ERROR] ${e.toString()}');
return null;
}
}
}
```