Function cgroup_stats 

pub fn cgroup_stats(reports: &[WorkerReport]) -> CgroupStats

Build per-cgroup telemetry (pure measurement, no assertions) from worker reports. This is the SINGLE telemetry builder on the assertion path: AssertPlan::assert_cgroup calls it unconditionally and assert_not_stuck wraps it with the default fairness checks, so per-cgroup CgroupStats is never gated behind whether a worker-check assertion was configured. Empty reports yield a num_workers == 0 CgroupStats (the reduces below collapse to 0.0/0), so a declared cgroup that collected no reports surfaces as a zero-worker entry rather than silently vanishing from ScenarioStats::cgroups.