rowKey method
Stable identity for rowIndex, used by selection and expansion.
Warning: The default implementation returns rowIndex, which is NOT
stable when rows are added or removed. If you use selection
(SummerRowSelection) or expandable rows (SummerRowExpandable),
must override this to return a stable identifier (e.g. a database ID
or UUID) so that the expanded/selected state survives row mutations.
Implementation
Object? rowKey(int rowIndex) => rowIndex;