ggml : hide ggml_object, ggml_cgraph, ggml_hash_set (#9408)

* ggml : hide ggml_object, ggml_cgraph, ggml_hash_set

ggml-ci

* ggml : add ggml-impl.h to backends

* ggml : fix compiler warnings

ggml-ci

* ggml : add assert upon adding nodes

ggml/src/ggml-vulkan.cpp

@@ -21,7 +21,7 @@
 #include <memory>
 #include <mutex>
 
-#include "ggml.h"
+#include "ggml-impl.h"
 #include "ggml-backend-impl.h"
 
 #include "ggml-vulkan-shaders.hpp"