Pubsub subscription blocking + ref counting

[aratz-lasa]

Two issues/bugs are detected in Wetware:

Pubsub subscription blocking

Sometimes when a client connects to a wetware server and iterates over a subscription the client does not exit the loop. Instead, it gets blocked forever.

Topic reference counting

Sometimes if you connect a client to a wetware server and you try to subscribe to a topic, you receive back pubsub.capnp:Topic.subscribe: topic already exists, which indicates an issue related to internal reference counting of topics. Currently, we have no info to reproduce this bug.

[lthibault]

This appears to happen across incompatible versions of Wetware. Closing (hopefully for good!)