loadJournal method
Restores undo/redo stacks from a journal payload.
Implementation
void loadJournal(Map<String, Object?> journal) {
final undo = journal[_undoKey];
final redo = journal[_redoKey];
_undoStack
..clear()
..addAll(_decodeCommandStack(undo));
_redoStack
..clear()
..addAll(_decodeCommandStack(redo));
if (maxEntries > 0) {
_trimToMax();
}
_trimTransactions();
}