Feature: Multiplayer support

[SokyranTheDragon]

Let me start off by saying - this is not a request, but an offer to implement it.

I've been commissioned to add support for Zetrith's Multiplayer (GitHub/Steam) to this mod. Originally, I planned to do it as an external patch. However, it would be significantly easier to implement native support.

In case of no interest in native support, I'd like to at least make a PR with a couple of changes that'd make it easier for me to make an external patch. The changes would have no effect on how the mod works - basically moving parts of code from existing methods into separate ones.

What would adding native support mean:

• Adding the Multiplayer API NuGet package .
• Creating a new class for a handful of Multiplayer related code and methods (in a new Compat directory?) - mostly to keep things organized and contained to single place.
• As I've mentioned earlier, moving parts of code from existing methods into separate ones.
• Adding SyncMethodAttribute to several methods in existing classes. This would be optional, it's just a more convenient way to handle it - the alternative is to call MP.RegisterSyncMethod(Type type, string name) or MP.RegisterSyncMethod(MethodInfo method) for each method that would have that attribute.

[simplyWiri]

You are welcome to open a pr, can ping me on discord if you would like me to review or respond in a more timely manner :+1: