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

src/engine/engine_io.h

@@ -69,6 +69,9 @@ void mj_makeModel(mjModel** dest,
 // copy mjModel; allocate new if dest is NULL
 MJAPI mjModel* mj_copyModel(mjModel* dest, const mjModel* src);
 
+// copy mjModel, skip large arrays not required for abstract visualization
+MJAPI void mjv_copyModel(mjModel* dest, const mjModel* src);
+
 // save model to binary file
 MJAPI void mj_saveModel(const mjModel* m, const char* filename, void* buffer, int buffer_sz);