The handling of cleanup is performed only the `Item_Set` method. This
was already correctly called for `DrawableCarouselBeatmapSet`, but not
for the class in question here.
This would cause runaway memory usage at song select when opening many
beatmaps to show their difficulties. For simplicity, we don't yet pool
these (and generate the drawables each time a set is opened) which isn't
great but likely will be improved upon when we update the visual /
filtering of the carousel. But this simplicity caused the memory usage
to blow out until exiting back to the main menu when cleanup would
finally occur.
`TestSceneHitObjectComposer.TestPlacementFailsWhenClickingButton()` was
attempting to cover the case of the user clicking a toolbox button which
was in front of the playfield, and ensure that the click did not result
in a placement. However, since the paddings in
67f83f246b were added, it is impossible
for a toolbox button to be in front of the playfield in the collapsed
state, which the test was relying on.
The test scenario is still however relevant in the case of the toolbox
being expanded, as in that state the toolbux buttons may very well end
up being in front of the playfield, and they still should not result in
a hitobject being placed. To ensure that this is the case, add a few
extra test steps ensuring that the toolbox is expanded first before
trying to retrieve an overlapping button.