add cuda gemv (#2400)

mlx/backend/cuda/gemv.h

@@ -0,0 +1,24 @@
+// Copyright © 2025 Apple Inc.
+
+#pragma once
+
+#include "mlx/backend/cuda/device.h"
+
+namespace mlx::core::cu {
+
+bool can_use_gemv(int M, int N, int K, bool a_transposed, bool b_transposed);
+
+void gemv(
+    const array& a,
+    const array& b,
+    array& out,
+    int M,
+    int N,
+    int K,
+    uint32_t batch_count,
+    const mlx::core::Shape& batch_shape,
+    const mlx::core::Strides& a_batch_strides,
+    const mlx::core::Strides& b_batch_strides,
+    CommandEncoder& encoder);
+
+} // namespace mlx::core::cu