narrow: delegate the narrow spec writing to the transaction This make it more transactional and will help us to simplify their backup. The implementation is not great, but it keep the patch simple as this is not the time for a larger refactoring yet.

narrow: get the narrow patterns from the repository object instead of disk Relying on disk data make the transactionally of this change complicated, so let us start reading data from other API instead.

narrow: widden the lock context in `tracking` The tracking configuration we modify must be read under lock. So we grab the lock sooner.

narrow: move `only_show` handling sooner in `tracked` This will help us to improve the locking scope in the `tracked` command.

tests: in test-fncache.t, be more tolerant to the "Killed" message format For example, on my box I'm seeing: $TESTTMP.sh: line 250: $pid Killed hg ci -qAm z

convert: use a priority queue for sorting commits, to make sorting faster To achieve this, we turn commit sorters into classes so they can encapsulate state. This reduces the sorting time from ~30s to ~10s on a 500k-commit prefix of a repo I tried to convert. (and probably reduces the time to sort the whole repo from many tens of minutes to minutes, but I didn't try that again) The date caching gets removed because priority queue already caches the key.

dirstate-v2: don't mmap the data file when on NFS `mmap` on NFS will trigger a SIGBUS when the mmap'ed file is deleted, which wouldn't work in our case. Also, the performance advantage of using mmap on NFS is debatable at best.

rust-dirstate: trace append/no append to help debugging