Implement TypeNamed to allow for consistent deserialization of metadata

Currently, a rebuild will potentially cause existing metadata naming to become invalid as `type_name` is unstable. This means that, between builds, metadata stored in corpora are not guaranteed to be loaded.

Instead, we should implement a trait, `TypeNamed`, which allows a structure to provide a consistent name. This should be implemented such that generic structures have different type names per monomorphisation by way of invoking `TypeNamed` implementations on its generic parameters. To be performant, this function should accept a `Write` type (e.g. `Vec`) and recursively invoke children.