fix(core): `save()` should be on internal kmx action queue

Fixes #7643.

The kmn statement `save()` action was being written directly to the
state queue, bypassing the internal kmx action queue. This caused two
issues:

1. save() actions were out-of-order with other actions on the same key
   event.
2. The number of items in the internal action queue became out of sync
   with the debug item queue, which would cause the debugger to fail
   with an assertion.

The new test in debug_api.cpp validates this second issue as the number
of items in the action queue now matches the expected count in the
corresponding debug item.