step_in tests: the cube fixture's edge directions clear of the assembly fixtures' ids

8eb93ff06 gave every cube edge its own line through two vertices, with the lines'
directions and vectors at #600 to #623. two_instance_assembly writes its occurrences
at #600 to #614, so 10 ids were defined twice, the reader kept the cube's, and the file
had no assembly: one body where hand_written_assembly,
later_instances_show_the_first_instances_mesh_placed and
repeated_items_are_shared_and_one_use_items_are_not expect two. The directions move to
#340 to #363, which no fixture uses.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/kernel/src/step_in/tests.rs

@@ -497,17 +497,18 @@ fn cube_entities() -> String {
     for (i, (x, y, z)) in pts.iter().enumerate() {
         s += &format!("#{}=CARTESIAN_POINT('',({x}.,{y}.,{z}.));\n#{}=VERTEX_POINT('',#{});\n", 200 + i, 210 + i, 200 + i);
     }
-    // 12 edges, each on the line through its two vertices (trimmed by them).
+    // 12 edges, each on the line through its two vertices (trimmed by them). Their directions
+    // and vectors are #340 to #363, clear of the ids the assembly fixtures add (#600 on).
     let edges = [(0, 1), (1, 2), (2, 3), (3, 0), (4, 5), (5, 6), (6, 7), (7, 4), (0, 4), (1, 5), (2, 6), (3, 7)];
     for (k, (a, b)) in edges.iter().enumerate() {
         let (p, q) = (pts[*a], pts[*b]);
         let d = (q.0 - p.0, q.1 - p.1, q.2 - p.2);
-        s += &format!("#{}=DIRECTION('',({}.,{}.,{}.));\n#{}=VECTOR('',#{},1.);\n", 600 + 2 * k, d.0, d.1, d.2, 601 + 2 * k, 600 + 2 * k);
+        s += &format!("#{}=DIRECTION('',({}.,{}.,{}.));\n#{}=VECTOR('',#{},1.);\n", 340 + 2 * k, d.0, d.1, d.2, 341 + 2 * k, 340 + 2 * k);
         s += &format!(
             "#{}=LINE('',#{},#{});\n#{}=EDGE_CURVE('',#{},#{},#{},.T.);\n",
             300 + k,
             200 + a,
-            601 + 2 * k,
+            341 + 2 * k,
             320 + k,
             210 + a,
             210 + b,