MLX - dynamic loading of mlx-c (#13735)

* MLX - dynamic loading of mlx-c

Create a wrapper layer to indirect the dependency on mlx-c so
the main ollama binary does not have a load-time dependency on mlx-c, mlx, and on linux, cuda.  Lazy load the library via dlopen
so we can adjust the path to ensure the dependencies are found
and fail gracefully if not present.

* review comments

* fix broken tests

x/ml/backend/mlx/mlx_dynamic.h

@@ -0,0 +1,26 @@
+// mlx_dynamic.h - Dynamic loading interface for MLX-C library
+#ifndef MLX_DYNAMIC_H
+#define MLX_DYNAMIC_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Initialize the MLX dynamic library
+// Returns 0 on success, -1 on failure
+int mlx_dynamic_init(void);
+
+// Get the last error message from dynamic loading
+const char* mlx_dynamic_error(void);
+
+// Check if MLX is initialized
+int mlx_dynamic_is_initialized(void);
+
+// Cleanup resources (optional, for clean shutdown)
+void mlx_dynamic_cleanup(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // MLX_DYNAMIC_H