tests: use the right python when running dummyssh for narrow some plateform no longer have a `python` executable. Differential Revision: https://phab.mercurial-scm.org/D9504

copies: avoid materializing a full directory map during copy tracing Materializing a full copy of every directory in a treemanifest repo can be quite expensive, even with a narrow matcher. For flat manifest repos, this should be equivalent - it will still materialize (and cache) a dict of all of the dirs inside of the manifest object, we just don't get a copy of it. In a repo I have here, this brings the time for a simple rebase from 11.197s to 4.609s. Differential Revision: https://phab.mercurial-scm.org/D9503