compilation failre with new mesh feature

The CI is giving the error
```
geom.c:1964:30: error: unknown type name 'mesh_bvh_node'
 1964 | static void bvh_node_set_box(mesh_bvh_node *node, const geom_box *box) {
```
which seems to stem from #74.  cc @Luochenghuang 