Opt-in reuse of Row instances when the data array identity changes

[johanrd]

perf-todo.md #20 mentions recreations of rows: createCoreRowModel memoizes on [table.options.data], so a new array replaces every Row and Cell even when the row objects in it are identical. That is intentional and tested, and the docs ask for stable references — but row identity is what React.memo, Vue keys and Glimmer {{#each}} keys compare, and caches (Apollo, React Query, sockets) hand you a fresh array per update.

React 19.3, react-table 9.2.4, 10 000 rows × 20 cols, 66 mounted, rows in React.memo with a stable getRowId:

update	today	with the opt-in
unrelated re-render	0	0
new array, identical row objects	1320	0
new array, one row changed	1320	20

1320 is every mounted cell, so the cost is the whole viewport whether one row changed or none.

Would an opt-in be welcome? reuseRowInstances: true keeps a Row when its id, original row object, index and parent are unchanged. Default off, so current behaviour and the test that asserts it are untouched.

Implementation sketch + tests, if it helps the discussion: johanrd#8 (all 1334 table-core tests pass). Happy to open a PR here if interest.