perf: split up and retire grammY runner

Most of the grammY runner perf comes from three things. They should be dealt with as follows.
- a good queue: this is useful for webhooks, too, so we should release it as a new plugin that works on both polling and webhooks
- backpressure by the queue: this can be added to the core lib, it is very simple to do so
- fast polling: this is actually trivial to do, we can also add it to the core lib with very little changes

That way, both polling and webhooks can be made substantially faster by adding a queue.