last second stats might miss the summarized quantile info

[filipecosta90]

If we end the benchmark without the last second having passed, we can loose that second quantile information.
The reason is because we push the last second data without summarizing it (we only summarize when we roll the second, in other words when that second is over).
offending line of code:
https://github.com/RedisLabs/memtier_benchmark/blob/104ed9f3fc9b51b77cef825636c185db0f30f8ab/run_stats.cpp#L153C23-L153C34