feat: initial eventbus implementation

[jaredallard]

Adds an eventbus package meant to make it easy to react to events synchronously. This will be used for chat integration as well as other places later on. Added tests for the eventbus package and started work on hooking it up into the proxy layer.

This will be considered complete when I move the whitelist system to use it. We will also potentially have a plugin system built into this to support these events over the wire instead of just in-memory.