remotefilelog: replace repack lock to solve race condition 2c74337e6483 reduced the probability of race-conditions when starting background repack and prefetch and we saw the difference in our CI instance with all failures disappearing except one where one call to waitonrepack seems to returns too early. I'm not sure what exactly goes wrong but I realized that while the prefetch operation uses a standard Mercurial lock, the repack operation is using a custom lock based on `fcntl.flock` on available platforms. As `extutil.flock` fallback on traditional Mercurial locks on other platforms and the tests are stable on my laptop, our CI environment and GCC112, I'm sending this patch to standardize the behavior across environments. Differential Revision: https://phab.mercurial-scm.org/D6844

perf: add a --stats argument to perfhelper-pathcopies The arguments will display some statisting about the distribution of the value we measure.

perf: add a --stats argument to perfhelper-mergecopies The arguments will display some statistics about the distribution of the value we measure.

archive: add XZ support if built with Python 3