Function custom_nested_cgroup_task_move 

pub fn custom_nested_cgroup_task_move(ctx: &Ctx<'_>) -> Result<AssertResult>

Move workers through nested hierarchy: sub -> parent -> cross-hierarchy sub -> parent.

The four cgroups (cg_0/sub with workers; cg_0, cg_1, and cg_1/sub as empty move targets) all persist for the full scenario — declaring them on the Backdrop is what lets every Step’s MoveAllTasks resolve the target cgroup without the previous Step’s teardown rmdir’ing it. Workers spawn inside cg_0/sub via CgroupDef; the empty peer cgroups go through Backdrop::extend_ops so no implicit worker spawn happens there.