Unit test for p2p hello protocol

I wish we had some tests for some of this newly introduced logic. It looks good to me, but I can't help but wonder when all of this complexity is going to regress and blow up on us. And how are we going to notice that.
What do you think?
Perhaps some of the state-independent pieces of logic could be moved to helpers and tested?
We could potentially test the bigger picture too, but I am unsure how mockable all of this currently is.

_Originally posted by @ruseinov in https://github.com/ChainSafe/forest/issues/4455#issuecomment-2203528778_