Add internal utility for zeroing int vectors.

PiperOrigin-RevId: 562608956
Change-Id: I25ff1bbf9abf8fe2a636ed1d728d10ae862e04c9

src/engine/engine_util_misc.h

@@ -119,6 +119,9 @@ MJAPI int mju_isBad(mjtNum x);
 // return 1 if all elements are 0
 MJAPI int mju_isZero(mjtNum* vec, int n);
 
+// set integer vector to 0
+MJAPI void mju_zeroInt(int* res, int n);
+
 // standard normal random number generator (optional second number)
 MJAPI mjtNum mju_standardNormal(mjtNum* num2);