Add mj_stackAllocInt to get correct size for allocating ints on mjData stack. Reducing stack memory usage by 10% - 15%.

PiperOrigin-RevId: 517672195
Change-Id: Ie14e6c9c99e8b9e1c5d3686b77631f2df0651c67

src/engine/engine_io.h

@@ -102,9 +102,12 @@ MJAPI void mj_resetDataKeyframe(const mjModel* m, mjData* d, int key);
 // mjData arena allocate
 void* mj_arenaAlloc(mjData* d, int bytes, int alignment);
 
-// mjData stack allocate
+// mjData stack allocate for array of mjtNums
 MJAPI mjtNum* mj_stackAlloc(mjData* d, int size);
 
+// mjData stack allocate for array of ints
+MJAPI int* mj_stackAllocInt(mjData* d, int size);
+
 // de-allocate data
 MJAPI void mj_deleteData(mjData* d);