4c Checkpoint format + reload validator

Checkpoint format + reload validator, partition-keyed via state_shape_hash, covering memories and registers for large simulation — see the LiveHD docs. (Absorbs the former 4g — checkpoint format + reload validator.)

Depends on

• 3c — partition-keyed via state_shape_hash.

Subtasks — pending

• A — checkpoint format + reload validator. Covers memories and registers for large simulation; partition-keyed via state_shape_hash (was 4g).

Subtasks — landed

None yet.