Merge t/01-{client,server} into a single file

There's not much reason to make these separate, and it saves on startup time.
Refactor to get rid of convoluted code

Timeouts should now throw a custom exception. Operative word is "should",
because there's still a bug where they don't work, which I can't figure out...
Explicitly return Nil from server/client threads

This gets rid of the weird error in the client part of 01-basic.t.
Sprinkle diag() in simple-socket.t

This file seems to deadlock randomly, this might help track down why.