add S2 Message Union type

[victorgarcia98]

Recently, I had the need to wrap the S2 messages in an envelope to simulate accelerated interactions between a CEM and a RM.

Nonetheless, for this to work, the message_type had to be a Literal. This PR refactors the code to use Literals instead of regular fields.

Example usage:

from pydantic import BaseModel, Field
from typing import Union, Annotated,Type, Literal
from datetime import datetime

from s2python.message import S2Message

class MetaData(BaseModel):
    dt : datetime

class S2Wrapper(BaseModel):
    message : S2Message = Field(discriminator='message_type')
    metadata : MetaData

[lfse-slafleur]

@victorgarcia98 Apologies for a late response. I do not work at TNO anymore and it took some time to get settled in my new situation again. Reviewing now!

[Flix6x]

As suggested, I removed all changes relating to the Literal issue. This PR now only contains the addition of the S2Message class and the renaming of the old S2Message class into S2MessageComponent.

(On a side note, Home Assistant has now released a version compatible with Pydantic v2. 😅 )

[lfse-slafleur]

Thanks for the addition! I added a couple of comments as examples but I believe we should be able to limit a number of types from S2MessageComponent to S2Message as only messages are expected there.

Fixed issues.

[Flix6x]

Approved by Víctor and I.