Make the data field of the Bounce and Bounced messages optional

[nepcore]

The data field in both the Bounce and Bounced messages are optional despite currently not being marked as such in the protocol documentation. ArchipelagoMW/Archipelago#5794 already exists to update the protocol documentation, but this is already happening in practice, for example in the CommonClient (ArchipelagoMW/Archipelago#5725). This PR changes the data fields of both affected messages to be optional.

[nex3]

This is already covered by #20, which makes BounceData::Generic's value an Option.

[nepcore]

Since that is currently a PR I assumed that that is not ready to be used yet. Please correct me if I'm wrong about that and I should already be using the refactor instead of the main branch.

Because the current CommonClient implementation sends Bounces with no data to the slot it's connected to every 100 seconds the current main branch experiences unexpected deserialization errors every couple minutes if for example Universal Tracker is connected to the same slot. Because of that it'd be great if this could be fixed for the current implementation while the refactor is being worked on.

[nex3]

I expect to land the refactor within a few days, so I don't think it's worth sliding changes in underneath it. In the meantime, if you need this, you can target your branch.

[nepcore]

Ok, thank you. I have already been targeting my branch, I just thought it might be helpful for others, but if the refactor is that close to done, then I'll close this and wait for that to land.