Make switch statements over enums in engine source use a typed expression to support compiler checking of full coverage.

PiperOrigin-RevId: 556854229
Change-Id: I36a5d146d776e10b946e2f9b51ace4ef3866471b

src/engine/engine_derivative_fd.c

@@ -153,7 +153,7 @@ void mj_stepSkip(const mjModel* m, mjData* d, int skipstage, int skipsensor) {
   }
 
   // use selected integrator
-  switch (m->opt.integrator) {
+  switch ((mjtIntegrator) m->opt.integrator) {
   case mjINT_EULER:
     mj_EulerSkip(m, d, skipstage >= mjSTAGE_POS);
     break;