Making `ObType` a separate crate

[samuelcolvin]

See https://github.com/samuelcolvin/rtoml/pull/59.

We should move ObType to a separate crate so it can be reused by other projects, there's also a chance that it allows one of us, or something else to come along and make it faster.

https://github.com/pydantic/pydantic-core/blob/a65f3272f002c7663c368aa4708ca706547e3bdb/src/serializers/ob_type.rs#L383-L428

[sydney-runkle]

This would probably be a good issue for me to pick up at some point in terms of comfort with the rust ecosystem 👍

[dylanbhughes]

Is this something still worth considering? I can take a crack at it

[davidhewitt]

I think there is still potential here, however I think the logic has been increasingly coupled to pydantic so I don't really know the likelihood of success.