rust: Keep lazily-initialized Changelog and Manifest log on the Repo object
That way if one of them is accessed multiple times it won’t be reopened
from the filesystem.
Differential Revision: https://phab.mercurial-scm.org/D11406
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state