toggleOnly method
Selects only item, deselecting all others (single-select helper).
Implementation
void toggleOnly(M3EDropdownItem<T> item) {
for (var i = 0; i < _items.length; i++) {
if (_items[i] == item) {
_items[i] = _items[i].copyWith(selected: !_items[i].selected);
} else if (_items[i].selected) {
_items[i] = _items[i].copyWith(selected: false);
}
}
_reapplySearchFilter();
notifyListeners();
onSelectionChange?.call(selectedItems);
}