Add compiler timing diagnostics to mjsCompiler, printed by compile.cc

For example, `compile mujoco_menagerie/robotis_op3/scene.xml` now outputs

```
Compile 1 (cold cache):
  total:      317.2 ms
  assets:     284.8 ms (wall clock)
    load:     616.1 ms
    hull:      26.4 ms
    poly:     137.8 ms
    inert:    177.8 ms
    bvh:      568.2 ms
    octr:       1.6 ms
    tex:       25.3 ms
  other:       32.4 ms

Compile 2 (warm cache):
  total:       79.9 ms
  assets:      54.5 ms (wall clock)
    load:     888.5 ms
    hull:       0.0 ms
    poly:       0.0 ms
    inert:      0.0 ms
    bvh:        0.0 ms
    octr:       0.0 ms
    tex:       21.4 ms
  other:       25.3 ms
```

PiperOrigin-RevId: 917850214
Change-Id: Iaec86230bec0faf2e47820e20cbff61de5b2621e

wasm/codegen/templates/bindings.cc

@@ -715,6 +715,10 @@ MjSpec::~MjSpec() {
 mjSpec *MjSpec::get() const { return ptr_; }
 void MjSpec::set(mjSpec *ptr) { ptr_ = ptr; }
 
+emscripten::val MjSpec::timer() const {
+  return emscripten::val(emscripten::typed_memory_view(9, mjs_getTimer(ptr_)));
+}
+
 std::unique_ptr<MjModel> mj_loadXML_wrapper_1(std::string filename) {
   char error[1000];
   mjModel *model = mj_loadXML(filename.c_str(), nullptr, error, sizeof(error));