Add WebSocket multiplayer for WASM builds

[sne11ius]

Let's be honest: this change is fully AI generated. I can understand if you want nothing to do with it.

But since it seems to work, I thought I should at least make you aware of the code.

[GMH-Code]

Hi @sne11ius ,

Thanks for the PR! I'll review it further and try it out when I get some time. I understand you say it's been AI generated and I'll look over it closely. To be fair though, after an initial look, it seems really promising, is tidy, and fits in really well with the rest of the project, so I'm taking it seriously.

You don't need to submit any further adjustments, but I might (possibly) add on top of it by making the ASYNCIFY build optional for people who only want to run single player and possibly limiting its scope in the build, simply because I prefer to avoid the stack instrumentation that comes with it. I'll handle that if necessary. Having seen the code though, I think that the impact's scope would end up being limited regardless and probably wouldn't affect the performance anyway.

I see you are only overriding the timing mode if the network code is in use, which I also appreciate, since I prefer not to lose vsync!

I'll review it and get back to you when I can!