Add configurable octree max depth for meshes.

The maximum depth of the octree used for SDF generation can now be specified in the mesh definition via `mjsMesh::octree_maxdepth`. The default value is 6.

PiperOrigin-RevId: 912494999
Change-Id: I6d828d1d3999b99d1210a6829a05b04fac591e1f

src/user/user_objects.cc

@@ -1285,7 +1285,7 @@ void mjCOctree::MakeOctree(const std::vector<Triangle*>& elements, const double
     }
 
     // skip if the box is empty
-    if (colliding.empty() || task.lev >= 6) {
+    if (colliding.empty() || task.lev >= max_depth_) {
       continue;
     }