Restructure include paths

include/backend/cuda/kernels/activation_functions.cuh

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <cuda_runtime.h>
+
+namespace CUDANet::Kernels {
+
+/**
+ * @brief Sigmoid activation function kernel
+ *
+ * @param src Pointer to the source array
+ * @param dst Pointer to the destination array
+ * @param len Length of the arrays
+ */
+__global__ void sigmoid(
+    const float* __restrict__ src,
+    float* __restrict__ dst,
+    const unsigned int len
+);
+
+/**
+ * @brief Relu activation function kernel
+ *
+ * @param src Pointer to the source array
+ * @param dst Pointer to the destination array
+ * @param len Length of the arrays
+ */
+__global__ void relu(
+    const float* __restrict__ src,
+    float* __restrict__ dst,
+    const unsigned int len
+);
+
+}  // namespace CUDANet::Kernels