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.
Merge pull request #11 from ventrebd/fix-#10444-mpi-archive-failure

Fix #10444: MPI archive failure

No, I wasn't sure enough of the impact of this change to want it in 1.57.  I just merged it now, we'll have 3 months to make sure it doesn't cause any problems.  I apologize for the delay.