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
