Make unsubscribe-inside-callback work in case of back-to-back updates #28
Description
The subscription handling added in #27 has a failing test unsubscribeInsideCallback_backToBackUpdates. That is — if you have a LiveObject that emits multiple updates one after another synchronously, then unsubscribing inside the first listener call will not prevent the listener from being called for the second update. This is a bit tricky to fix given the mutable-state-struct approach that I've taken for storing the subscriptions (didn't think of this issue at the time). Don't think it's a high priority to fix, given that a given LiveObject coalesces its updates anyway so I don't think it'll ever be emitting multiple updates synchronously. And we might revisit how we do unsubscribe-inside-callback anyway.