Add mjv_copyModel to copy mjModel, skipping large arrays not required for abstract visualization.

This functionality is meant for fast copying of `mjModel` when synchronizing the visualization state, as in the Python passive viewer.

PiperOrigin-RevId: 699199743
Change-Id: I13a5160063eb09139ec1aee9c4969bc1c6f547f1

include/mujoco/mujoco.h

@@ -692,6 +692,9 @@ MJAPI int mjv_updateSceneFromState(const mjvSceneState* scnstate, const mjvOptio
                                    const mjvPerturb* pert, mjvCamera* cam, int catmask,
                                    mjvScene* scn);
 
+// Copy mjModel, skip large arrays not required for abstract visualization.
+MJAPI void mjv_copyModel(mjModel* dest, const mjModel* src);
+
 // Set default scene state.
 MJAPI void mjv_defaultSceneState(mjvSceneState* scnstate);