Remove class-name dispatch in RemoteLogMetadataSerde

The RemoteLogMetadataSerde#serialize receives a RemoteLogMetadata object, and has to dispatch to one of four serializers depending on it's type. This is done by taking the class name of the RemoteLogMetadata and looking it up in maps to find the corresponding serializer for that class.

This later requires an unchecked cast, because the RemoteLogMetadataTransform is generic. This is all type-unsafe, and can be replaced with type-safe if-elseif-else statements that may also be faster than the double-indirect map lookups.