fix: selection race condition (#1194)

* fix: guard debounced desktop selection update

Avoid dereferencing a cleared selection from the delayed
macOS metrics callback and add a regression test that
covers the stale-timer path.

* chore: clean up analyzer warnings

Remove redundant default arguments in tests and apply the
missing trailing comma required by the current lint rules.

test/legacy/undo_manager_test.dart

@@ -427,7 +427,6 @@ void main() async {
       transaction,
       options: const ApplyOptions(
         recordUndo: false,
-        recordRedo: false,
         source: TransactionSource.none,
       ),
     );