Control vector loading fixes (#8137)

* Fixed leak in llama_control_vector_load_one() and allow llama_control_vector_load() to grow

* refactored `llama_control_vector_load_one()`

* allow multiple directions for same layer in same file

* llama_control_vector_load_one() and llama_control_vector_load() now break on error

* removed unnecessary ggml_free() call