* ggml: new optimization interface
remove test2.c, test3.c
store adamw params in tensor
move grads from tensor to graph
* avoid segfault upon API misuse
* add ggml-opt.h to public headers
* remove dependence of ggml-opt.cpp on ggml-cpu.h
This commit removes the buffer_id field from the leaf_alloc struct.
The motivation for is that this field is only written to and never
read/used as far as I can tell. Each tensor_alloc has a buffer_id field
and this is what caused me to look into this more closely, to
understand what the buffer_id in leaf_alloc was used for.
