`:ConnectOnce` should return the ScriptConnection

[lucasmz-dev]

I don't know whether to add this or not, as with deferred events, the behaviour is a little more 'open in the air', if it was fired but it still didn't run still because it has been deferred, you can't tell if the handler will actually be run or not with a .Connected value.

It only gets actually disconnected after the handler runs, it just doesn't run the function you give it.

One solution, which was already a thing in older versions with :Wait, is disconnect as you fire the connection. Integrate it with the connection data, if that connection is supposed to be disconnected right away or not, only problem here is that it would require extra indexing which I'm not exactly interested by, but it should be a small cost to CPU so... it's up in the air.