Function setup_cgroups 

pub fn setup_cgroups<'a>(
    ctx: &'a Ctx<'_>,
    n: usize,
    wl: &WorkloadConfig,
) -> Result<(Vec<WorkloadHandle>, CgroupGroup<'a>)>

Create N cgroups, spawn workers in each, and start them.

Returns the worker handles and an RAII CgroupGroup that removes the cgroups on drop. Workers are moved into their target cgroups before being signaled to start.