// Find the longest-idle connections in 2 categories:
    //
    //  1. OLD: Connections that have been idle for at least keepAliveDurationNs. We close these if
    //     we find them, regardless of what the address policies need.
    //
    //  2. EVICTABLE: Connections not required by any address policy. This matches connections that
    //     don't participate in any policy, plus connections whose policies won't be violated if the