dirstate: use `dirstate.change_files` to scope the change in `copy`

This is the way, unless we are not actually touching the working copy.
In such cases we don't need to do something.

mercurial/commands.py

@@ -2497,7 +2497,19 def copy(ui, repo, *pats, **opts):
     Returns 0 on success, 1 if errors are encountered.
     """
     opts = pycompat.byteskwargs(opts)
-    with repo.wlock():
+
+    context = repo.dirstate.changing_files
+    rev = opts.get(b'at_rev')
+    ctx = None
+    if rev:
+        ctx = logcmdutil.revsingle(repo, rev)
+        if ctx.rev() is not None:
+
+            def context(repo):
+                return util.nullcontextmanager()
+
+            opts[b'at_rev'] = ctx.rev()
+    with repo.wlock(), context(repo):
         return cmdutil.copy(ui, repo, pats, opts)