Consider doing K rounds of N iterations

[WillSewell]

Instead of doing N iterations with the same "channel" structure, I would like to do K rounds of N iterations, with each round allocating a new channel structure and forgetting about the new one. My intuition is that this would reveal latencies associated with deterministic reference-counting that are currently hidden from the benchmark while they may manifest themselves in realistic program. But I haven't actually experimented with it to check it; if there is no counting-collection pause time, it may not be worth the extra complexity.