Non-effectful serialization and deserialization

[svroonland]

This is an exploration of #853.

Serializers cannot fail, like in zio-json. Deserialization is no longer allowed to be side-effectful, so serializers like the Confluent Avro serde (which communicates with a schema registry) will have to be run in the user's own code. We should add an example to the documentation.

I thought a free error type for the deserialization error would be nice, but at some point it has to be integrated with other errors in the Runloop, which means wrapping it in an exception for now. Needs something better..