Fix enum serialization problems

[jduerholt]

As outlined here https://stackoverflow.com/questions/69541613/how-to-json-serialize-enum-classes-in-pydantic-basemodel, the json module has problems with serializing plain enums, so far we had to use always pydantics model_dump_json. This can lead to problems and confusion.

Setting up enums which also inherit from str solves this issue. In py3.11 is a new datatype available which does exactly this called StrEnum (https://docs.python.org/3/library/enum.html#enum.StrEnum). But due to backwards compatibility, I implemented the solution to explicitly inherit from str.

[bertiqwerty]

Thanks Johannes. What do you mean with

so far we had to use always pydantics model_dump_json. This can lead to problems and confusion.

?

[jduerholt]

The problem is that if you do not change it in this way, pydantic serializes it to "EnumA.ValueA", if you pass default=str to json.dumps, it is able to serialize the enum but it gives you just ValueA. With the changes, you do not have to pass default=str, and both serialize in the same way. I had problems with both working with requests and using TinyDB to store bofire based documents and get it back from the storage. This PR solves it.

[bertiqwerty]

Does it work with old BoFire objects that already have been stored somewhere?

[jduerholt]

Could lead to some Problems. But I think it is still good to merge it in, as this creates in general less problems. One can write a two liner to fix the old jsons.