strip: make tree stripping O(changes) instead of O(repo) The old tree stripping logic iterated over every tree revlog in the repo looking for commits that had revs to be stripped. That's very inefficient in large repos. Instead, let's look at what files are touched by the strip and only inspect those revlogs. I don't have actual perf numbers, since internally we don't use a true treemanifest, but simply iterating over hundreds of thousands of revlogs takes many, many seconds, so this should help tremendously when stripping only a few commits.