Rebuild annotation model while parsing annotations

Under some scenarios, nomad.datamodel.metainfo.annotations.ELNAnnotation model was not fully defined.

This only happened while trying to run the nomad app via a plugin dependency (local dev, oasis, central installation worked fine), not really sure what the root cause is here.

To be on the safe side, in this MR we rebuild the AnnotationModel before calling the model_validate function.