feat(stability): refine timing to ensure numerical stability of performance measurements

[zigzagcai]

Hi developers @simonguozirui @anneouyang ,

Thanks for such a great project! We found numerical stability issue of kernel performance measurements in real world use case.

For small kernels, the returned list of forward elapsed times typically varies a lot (usually due to kernel launch overhead), and an outlier can greatly affect the mean or median timing. Even small deviation in kernel runtime will affect the benchmark result and reward in RL scenarios.

So, we need to guarantee numerical stability of performance measurements.

Therefore, we assume that a certain proportion of data points in multiple measurements are outliers, and by removing them from the list, we can obtain stable performance measurements.