Fix #10444: MPI archive failure

Add "const" to save_override for archive::class_id_type and archive::version_type.  WIthout it, they do not participate in overload resolution when called with a const argument, and the default template function is called.  This leads to saving 4 bytes for archive::version_type, but only loading 1 -- all subsequent load operations are then off by 3 bytes.