Add time boxed sampler implementation

[Max Penet]

right now we just have a simple ring buffer, if requests stop and start again hours later we'd still be stuck on the same limit with the windowed sampler, which might be ok in most cases, but not always, so timeboxing values could be a good improvements, we could just store tuples of [T, RTT] and purge them periodically (or on avg computations since we walk them anyway)