Fix rollup computation from hierarchy widget

What does this MR do and why?

When dragging items in the hierarchy widget to change the parent of a work item, we must trigger rollup computation for both old and new parents

References

Screenshots or screen recordings

Before	After
Screen_Recording_2025-08-21_at_2.28.46_AM	Screen_Recording_2025-08-21_at_2.54.30_AM

How to set up and validate locally

1. Enable the use_cached_rolled_up_weights feature flag
2. In the "Child items" widget of an epic, move a child item with weight from one parent to another
3. Refresh the page. The old and new parents should show the correct rolled up weight

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