docs: private Map<CPGroupId, Collection<Tuple2<Long, Long>>> getSessionsToExpire() {
          Map<CPGroupId, Collection<Tuple2<Long, Long>>> expired = new HashMap<CPGroupId, Collection<Tuple2<Long, Long>>>();
          for (RaftSessionRegistry registry : registries.values()) {
              Collection<Tuple2<Long, Long>> e = registry.getSessionsToExpire();
              if (!e.isEmpty()) {
                  expired.put(registry.groupId(), e);
              }
          }
  
          return expired;
      }