Image Trace: a closed seam run is the subpath itself

#7814 made SubPath::anchors an Anchors, and #7810's seam fills, merged in the same batch,
passed it to SubPath::new, which takes a Vec, so vectorcraft-trace doesn't compile on main.
A closed subpath whose every segment is marked is its own run: clone it.

crates/trace/src/seam.rs

@@ -84,7 +84,7 @@ fn fills(paths: &[TracedPath]) -> Vec<TracedPath> {
                 continue;
             }
             if sp.closed && marks.iter().all(|&m| m) {
-                runs.push(SubPath::new(sp.anchors.clone(), true));
+                runs.push(sp.clone());
                 continue;
             }
             // Start after an unmarked segment, so that a run across the subpath's first anchor