@Override
        public int hashCode() {
            return (ipOrHost.hashCode() * 31 + port) * 31 + Boolean.hashCode(isHttp1);
        }
Cleans up empty entries with no activity for more than 1 minute. For reduced overhead, we perform this
only when 1) the last clean-up was more than 1 minute ago and 2) the number of acquisitions % 256 is 0.
core/src/main/java/com/linecorp/armeria/client/DefaultEventLoopScheduler.java