Disconnection hooks #179
Description
A requested feature is to run arbitrary logic once we know a certain peer has disconnected. For example, we might drop other requests that are being processed right now, or update some metrics etc etc.
For now, we should try to add it at least for req/rep sockets. The implementation should build on the ideas developed in #177 that introduces the concepts of hooks. Up to the implementer whether hook logic should be moved to a separate crate or not.