bblfshd and go-client interdependency

[ncordon]

bblfshd imports go-client here, and probably in other places, but at the same time go-client needs the bblfshd to be running in order to work. This is a cycle in dependencies that may be worth exploring and solving (in case it is a bug).

[creachadair]

I believe it's not a strict cycle: bblfshd has a static dependency on some of the client library's support code, but I think not the client itself. The opposite is a runtime (RPC) dependency.

That said: This probably does mean we could factor out the shared code as a separate package, even if it continues to live in the client repo.