perf(globe): less churn in movers and lines

Review of Tasks 2–3:
- the mover store's instance checks no longer build arrays or closures
  per set() (orientation and colour checked field by field), and dirty()
  returns one reused range object;
- Cesium models get their matrix and colour through scratch objects
  (Model.modelMatrix and Model.color copy what they are given) instead
  of a new Matrix4 and Color per placement;
- a destroyed MoverSet releases its store (count 0, empty instance
  arrays, no pick ids) so a set object a layer still holds keeps no
  memory, and the Cesium parts drop their billboard, point and model
  lists;
- (with the overlay commit) the Navara line viewport is updated in
  place.

Node micro-measure, 10 000 instances set + packed per frame: 0.27-0.29
ms, about 1.7 KB per frame (0.17 B per instance), as before. Contract:
Cesium 70/70, Navara 76/76.

src/globe/movers.test.mjs

@@ -170,7 +170,7 @@ test('the set facade forwards to the store and an engine commit, once destroyed
   );
   const calls = [];
   const set = createMoverSet(store, {
-    commit: () => calls.push(['commit', store.dirty()]),
+    commit: () => calls.push(['commit', { ...store.dirty() }]),
     destroy: () => calls.push(['destroy']),
   });
   set.set(0, { position: { x: 1, y: 2, z: 3 } });
@@ -187,3 +187,23 @@ test('the set facade forwards to the store and an engine commit, once destroyed
   assert.throws(() => set.set(0, {}), /destroyed/);
   assert.throws(() => set.commit(), /destroyed/);
 });
+
+test('a destroyed set releases its instance arrays', () => {
+  const store = createMoverStore(
+    normalizeMoverSetOptions({
+      id: 'r',
+      kind: 'point',
+      capacity: 1000,
+      point: { sizePx: 2 },
+    }),
+  );
+  const set = createMoverSet(store, { commit() {}, destroy() {} });
+  set.set(0, { position: { x: 1, y: 2, z: 3 }, pickId: 'p' });
+  set.setCount(1);
+  set.destroy();
+  assert.equal(store.count, 0);
+  assert.equal(store.positions.length, 0);
+  assert.equal(store.pickIds.length, 0);
+  assert.equal(set.positionsView().length, 0);
+  assert.equal(store.dirty(), null);
+});