The misuse of smart union in pydantic about docarray

[hanxiao]

This to be honest is an upstream issue, i don't think we can solve it?

[numb3r3]

One possible quick solution is to disable the smart union in the pydantic model definition

class PydanticDocument(BaseModel):
    ...
    tags: Optional[Dict[str, '_StructValueType']] -> tags: Optional[Dict[str, ANY]]

https://github.com/jina-ai/docarray/blob/main/docarray/document/pydantic_model.py#L30-L50

But I'm not very clear whether this change will not destroy other API/functions.

[numb3r3]

With this PR #73, we can get the following result

origin:
{'a': '1', 'b': 1, 'c': '2'}
pydantic: 
{'a': '1', 'b': 1, 'c': '2'}
protobuf: 
{'b': 1.0, 'c': '2', 'a': '1'}
jsonschema
{'b': 1.0, 'c': '2', 'a': '1'}