Bug: Bug serializing and deserializing with nested Union of BaseDocs #1553

from docarray import BaseDoc
from docarray.documents import TextDoc, ImageDoc
class CustomDoc(BaseDoc):
    ud: Union[TextDoc, ImageDoc] = TextDoc(text='I am in union')

docs = DocList[CustomDoc]([CustomDoc( ud=TextDoc(text='I am in union'))])

DocList[CustomDoc].from_protobuf(original_docs.to_protobuf())