Save/restore is now fully implemented in the hybrid interpreter. Updated
open question 7 to reflect completion, marked the what-to-do-next item as
done, and updated the milestone section to include save/restore in the
"what works" list.
Also noted the QuetzalParser off-by-one bug fix (return_pc parsing).
op_save is a stub that always fails. QuetzalWriter chunks are stubs.
Added as open question 7, next step item, and corrected the inaccurate
claim that save/restore works.
The hybrid interpreter can now run Zork 1, marking the first working
implementation of the embedded interpreter path. This enables levels 2-5
(inspectable/moldable/shared worlds) rather than just the opaque terminal
approach of level 1.
