only use `self.stack.top()` when we need to store `Arc<Page>` in struct
```sh
Execute `SELECT count() FROM users`/limbo_execute_select_count
time: [5.3733 µs 5.3801 µs 5.3881 µs]
change: [-34.047% -33.949% -33.851%] (p = 0.00 < 0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) high severe
```
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#2962
088cb449a5