`mark_dirty_trees` skips live entities after entity-index reuse

## Bevy version and features

- Verified against both `0.19.1` and `main`
- Default `multi_threaded` enabled

## What you did, what went wrong

In my project I despawn and then respawn entities in the same frame so scene is consistent with user's input. Occasionally, during testing, I would notice that the mesh at the world origin would render incorrectly, either missing faces or rendering z-fighting faces. I nailed the problem down to the multi-threaded `mark_dirty_trees` code path. I'm currently using `StaticTransformOptimizations::Disabled` as a workaround.

## Additional information

I've prepared a minimal reproduction where this problem can be observed on every run:
https://gist.github.com/tnajdek/e945d7a6f52db525d46d913e12f89873

I believe the visited bitset in `mark_dirty_trees` deduplicates by entity index rather than the full generational Entity. Because `RemovedComponents` can yield stale IDs for despawned entities, a stale ID can set the bit for a live entity that reused its index, causing the live traversal to stop at the leaf without dirtying its parent.

Run the minimal reproduction linked in the issue with default multi_threaded settings, then inspect the multi-threaded mark_dirty_trees path and its visited-bitset handling. The fix is complete when despawn-and-respawn entity-index reuse no longer leaves the live hierarchy undirtied and the reproduction stops showing missing or z-fighting faces.

Written by the indexing model from the issue text.