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

doc/APIreference/APItypes.rst

@@ -828,6 +828,18 @@ Type of built-in procedural mesh.
 .. mujoco-include:: mjtMeshBuiltin
 
 
+.. _mjtCTimer:
+
+mjtCTimer
+~~~~~~~~~
+
+Compiler timing categories, used in :ref:`mjs_getTimer`. Top-level timers (``TOTAL``, ``ASSETS``) measure wall-clock
+time. Asset sub-timers measure CPU time summed across all assets; with multi-threaded compilation their sum can exceed
+the ``ASSETS`` wall-clock time.
+
+.. mujoco-include:: mjtCTimer
+
+
 .. _tyPluginEnums:
 
 Plugins

doc/APIreference/functions.rst

@@ -2079,6 +2079,15 @@ Write [datetime, type: message] to MUJOCO_LOG.TXT.
 
 Get compiler error message from spec.
 
+.. _mjs_getTimer:
+
+`mjs_getTimer <#mjs_getTimer>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. mujoco-include:: mjs_getTimer
+
+Get compiler timing diagnostics from spec, returns pointer to array of size mjNCTIMER.
+
 .. _mjs_isWarning:
 
 `mjs_isWarning <#mjs_isWarning>`__