Split global marshaller into Persistence and Internal marshaller

Currently the internal marshaller is used for marshalling key/value/metadata in store implementations. This means that it is possible for internal classes to be marshalled to a user store, which can cause compatibility issues if an internal classes serialization format changes (due to marshaller changes or addition/removal of fields).

We should separate the internal and persistence marshaller, only exposing the latter to stores via the InitializationContext. The persistence marshaller should only be able to serialize user key/values and the metadata/version data.