In no particular order: - fixing the `~objects` - creating a `BasicEventLoop` implementation using standard mutexes and condition variables and converting some of the primitive `Scheduler` tests to use it - creating a runtime API for spawning the runtime and/or schedulers with a custom `EventLoop` - reviewing `PausibleIdleCallback` to determine if it's too uv-specific would be nice to have another event loop (besides libuv) to use to flesh this out. Related to #4419