@Override
    public String toString() {
        return "ChannelReceiver{value=" + this.value + ", timestamp=" + this.timestamp + ", expiryMillis=" + this.expiryMillis + '}';
    }
Gets the timestamp when the last value was received.

@return the last received timestamp
helper/src/main/java/me/lucko/helper/messaging/util/ChannelReceiver.java