add tool to allow plotting tensor allocation maps within buffers

ggml/include/ggml-backend.h

@@ -208,6 +208,9 @@ extern "C" {
     // Set a callback to be called for each resulting node during graph compute
     GGML_API void                 ggml_backend_sched_set_eval_callback(ggml_backend_sched_t sched, ggml_backend_sched_eval_callback callback, void * user_data);
 
+    // internal
+    GGML_API struct ggml_cgraph * ggml_backend_sched_get_graph_copy(ggml_backend_sched_t sched);
+
     //
     // Utils
     //