test: introduce libp2p-swarm-test

This patch-set introduces `libp2p-swarm-test`. It provides utilities for quick and safe bootstrapping of tests for `NetworkBehaviour`s. The main design features are:

- Everything has timeouts
- APIs don't get in your way
- Minimal boilerplate

Closes #2884.

Pull-Request: #2888.

protocols/gossipsub/src/behaviour.rs

@@ -3689,7 +3689,7 @@ mod local_test {
     use super::*;
     use crate::IdentTopic;
     use asynchronous_codec::Encoder;
-    use quickcheck::*;
+    use quickcheck_ext::*;
 
     fn empty_rpc() -> Rpc {
         Rpc {