Feature request: timeout argument for `client.sample`

Similarly to #4, it would be useful to be able to back out of sampling without needing to wrap things in a thread or use an executor. I agree that in many cases, you'd want to sample asynchronously to maximize throughput, but there are cases where the predictability and simplicity are preferable even if comes at the expense of efficiency (e.g., in research). A timeout argument would simplify the synchronous setting without sacrificing safeguards from indefinite waiting.