pullbundle: add some information on the cached change This also adds a way to skip "caching" smaller range in the debugcommand (not in the extensions itself).

pullbundle: add data about the cached bundle size and hit

pullbundle: add a command to generate cache hit statistic This new command should help checking that the stable range produce reusable bundle.

pullbundle: point out the output flooding issue from core Right now, we don't have a reliable progress report when using pullbundle.

pullbundle: issue local branches in the right order

pullbundle: delay cache file opening Otherwise we can end-up with a too many file open at the same time.