[adario]

Description

Fixes two bugs in ShapeHitbox when a hitbox is removed and re-added:

• Stale bounds: _validAabb is only reset by the transform listeners, which onRemove
  detaches. If an ancestor moves while the hitbox is removed, the re-added hitbox keeps its old
  aabb, so the broadphase, raycast, containsPoint and the collision callbacks use the old
  position. This also happens when the hitbox is removed and added again together with its
  parent. onMount now marks the bounds as invalid.
• Growing ancestor list: onMount appends to _transformAncestors and never clears it, so
  each re-mount adds the ancestors again and onRemove walks the whole list. onRemove now
  clears it.

A hitbox that fills its parent (no explicit size) hid the first bug, since filling the parent
recomputes the bounds on mount.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• [-] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [-] I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Related Issues

Closes #4141