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

include/mujoco/mjspec.h

@@ -129,6 +129,24 @@ typedef enum mjtOrientation_ {     // type of orientation specifier
 } mjtOrientation;
 
 
+typedef enum mjtCTimer_ {          // compiler timing categories
+  // top-level timers (wall-clock)
+  mjCTIMER_TOTAL = 0,              // total compile time
+  mjCTIMER_ASSETS,                 // asset compilation
+
+  // asset sub-timers (CPU time, summed across all assets)
+  mjCTIMER_TEXTURE,                // textures
+  mjCTIMER_MESH_LOAD,              // mesh: file loading
+  mjCTIMER_MESH_HULL,              // mesh: convex hull
+  mjCTIMER_MESH_POLYGON,           // mesh: normals and polygons
+  mjCTIMER_MESH_INERTIA,           // mesh: volume, CoM, inertia
+  mjCTIMER_MESH_BVH,               // mesh: bounding volume hierarchy
+  mjCTIMER_MESH_OCTREE,            // mesh: octree and SDF
+
+  mjNCTIMER                        // number of compiler timers
+} mjtCTimer;
+
+
 //-------------------------------- attribute structs (mjs) -----------------------------------------
 
 typedef struct mjsElement_ {       // element type, do not modify

include/mujoco/mujoco.h

@@ -1005,6 +1005,9 @@ MJAPI void mju_writeLog(const char* type, const char* msg);
 // Get compiler error message from spec.
 MJAPI const char* mjs_getError(mjSpec* s);
 
+// Get compiler timing diagnostics from spec, returns pointer to array of size mjNCTIMER.
+MJAPI const double* mjs_getTimer(mjSpec* s);
+
 // Return 1 if compiler error is a warning.
 MJAPI int mjs_isWarning(mjSpec* s);