add msgspec

[Vizonex]

What do these changes do?

I saw that this library was using msgspack so I felt like adding something of my own as well. Msgspec is one of the fastest python dataclass libraries out there because it's written in C and with it having it's own msgspack protocol I decided to add in an encoder and decoder.

Are there changes in behavior for the user?

I attempeted to make sure that my end was properly typehinted.
I'm going to convert this into a draft for now but hopefully maybe I can turn it into a real pull request.

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes

[Dreamsorcerer]

I'm not sure we want to be adding more dependencies here. As per other requests for new backends, we should probably put any other serializer in a new library (or a component in the parent library, if they're interested) and have it maintained there.

At the same time, a user wanting this could just implement the custom serializer in a couple of lines of code..