Enable compiler errors for implicit switch case fallthroughs.

Also unify warning options across Clang and GCC and fix minor issues that was surfaced by this.

PiperOrigin-RevId: 508619655
Change-Id: I59b777bf2dfea4422485670e2427c7d3f5cf6405

src/engine/engine_vis_visualize.c

@@ -62,6 +62,7 @@ static void makeLabel(const mjModel* m, mjtObj type, int id, char* label) {
 
   // copy result into label
   strncpy(label, txt, 99);
+  label[99] = '\0';
 }