Refactors serialize and deserialize value to switch/function pattern.

This is a pattern we have used frequently (e.g. in ReferenceResolvingExecutor's evaluate method) to persist more  information in traces.

Currently a little difficult to narrow down hotspots in serialization code.

Additionally adds PyType annotations and cleans up the contracts a little bit, easier with this new factorization.

PiperOrigin-RevId: 322246977