lfs: convert to using exthelper to wrap functions
I'm not 100% sure that upgraderequirements() can be double annotated safely, but
it seems OK based on printing the address of the function being wrapped.
One thing I've noticed is that @eh.reposetup doesn't do the usual check to
ensure that it's a local repo. Should that be baked into @eh.reposetup()
somehow, possibly with a non-default option to skip the check? It seems like a
gaping hole if every function that gets registered needs to add this check.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
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any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).