Cleanup the PingRequestResponseDirective

[ktoso]

It is not easy to act on and implementations end up using default: to ignore most cases:

    public enum PingRequestResponseDirective {
        case gossipProcessed(GossipProcessedDirective)

        case alive(previousStatus: SWIM.Status) // TODO: offer a membership change option rather?
        case nackReceived
        /// Indicates that the `target` of the ping response is not known to this peer anymore,
        /// it could be that we already marked it as dead and removed it.
        ///
        /// No additional action, except optionally some debug logging should be performed.
        case unknownMember
        case newlySuspect(previousStatus: SWIM.Status, suspect: SWIM.Member)
        case alreadySuspect
        case alreadyUnreachable
        case alreadyDead
        /// The incoming gossip is older than already known information about the target peer (by incarnation), and was (safely) ignored.
        /// The current status of the peer is as returned in `currentStatus`.
        case ignoredDueToOlderStatus(currentStatus: SWIM.Status)
    }

it should rather have gossip processed and emit change? if a change is to be emitted and additional information but only informational what the status is now