Connectedness events are not submitted by mocknet

[Wondertan]

After #1574, the Network is now responsible for emitting such events. However, only Swarm was updated to emit them, and the only second implementation, mocknet was not. There are projects in the ecosystem that uses mockent and for whom updating to v0.27 will break tests because of this.

Additionally, the tests that depend on swarm/testing will break as well due to the reason @vyzo mentioned in here. The user now has two instantiate the EventBus themselves and pass two both the host constructor and the GenSwarm, but if I understand correctly this is part of a larger issue #1993.

[marten-seemann]

mocknet is unmaintained and only kept for backwards compatiblity. If you want to submit a fix though, I'd be happy to review.

[Wondertan]

I am sure Lotus depends on it, and they will likely want to update to v0.27.

I can submit a patch but in weeks from now.

[Wondertan]

Why is it unmaintained?
Should we deprecate it and remove it in a few releases if it is unmaintained? Similar issues will likely happen in the future where mocknet is forgotten to be updated in a breaking way.

[MarcoPolo]

Thanks for the PR, I'll review :)

What do you think about a in-memory transport? It would let us run all the same code as normal, but use Go channels/runtime to do the actual network part of it. It'll probably behave more realistically and use less code than mocknet.

For prior art, rust-libp2p has an in-memory transport.