This removes dependencies on swarm/testing and the blank host.
1. swarm/testing really shouldn't be used at all except for internal
libp2p stuff.
2. The blank host should only be used in _very_ special cases (autonat,
mostly).
* cleanup: fix vet failures and most staticcheck failures
* Fix remaining staticcheck failures
* Give test goroutines chance to exit early when context is canceled
When the WithDiscovery option is passed to PubSub then PubSub will be able to search for more peers that are interested in our topics.
This includes the ability for Publishes (via Topic.Publish()) to block until the router is ready to publish. When a router is ready is currently defined by a combination of a user defined MinTopicSize function (passed into topic.Publish via the WithReadiness publish option) and the properties of the pubsub router used. The discovery tests show example usage.
