Align `PackedDataChecksum::process` code path with `save` code path
- in PackedDataChecksum, re-use the
save
infrastructure to make sure that by construction the checksum is computed on exactly the same data that is actually saved as it now uses the same implementation - remove the
as_tuple
infrastructure which is no longer required
note: sits on top of !3244 (closed) which fixes a lifetime issue in as_tuple
-- so where !3244 (closed) fixes a bug, this eliminates the code in question...
Edited by Gerhard Raven