reset method
Resets focus to initial state (first item, clears all errors).
Implementation
void reset({int initialIndex = 0, bool clearErrors = true}) {
if (_itemCount == 0) {
_focusedIndex = 0;
} else {
_focusedIndex = initialIndex.clamp(0, _itemCount - 1);
}
if (clearErrors) clearAllErrors();
}