CUDA backend: backbone (#2075)

mlx/backend/cuda/slicing.cpp

@@ -0,0 +1,15 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/backend/gpu/slicing.h"
+
+namespace mlx::core {
+
+void concatenate_gpu(
+    const std::vector<array>& inputs,
+    array& out,
+    int axis,
+    const Stream& s) {
+  throw std::runtime_error("concatenate_gpu not implemented in CUDA backend.");
+}
+
+} // namespace mlx::core