llama : add option to save memory in device buffers (#22679)

* llama : add option to save memory in device buffers

* tests : extend llama-save-load-state

src/llama-io.h

@@ -12,7 +12,7 @@ public:
     virtual ~llama_io_write_i() = default;
 
     virtual void write(const void * src, size_t size) = 0;
-    virtual void write_tensor(const ggml_tensor * tensor, size_t offset, size_t size) = 0;
+    virtual void write_tensor(ggml_tensor * tensor, size_t offset, size_t size) = 0;
 
     // bytes written so far
     virtual size_t n_bytes() = 0;