Function arrangement_sizes_expired_retractions 

fn arrangement_sizes_expired_retractions(
    rows: impl IntoIterator<Item = (Row, i64)>,
    cutoff_ts: u128,
    item_id: CatalogItemId,
) -> Vec<BuiltinTableUpdate>

Returns retraction updates for rows in a consolidated mz_object_arrangement_size_history snapshot whose collection_timestamp (column 3) is strictly before cutoff_ts.

Panics if any input row has diff != 1: the caller must consolidate first, and a consolidated history table should never contain retractions because the only source of retractions is this function itself.