chore: import upstream snapshot with attribution

kt-kernel/operators/moe_kernel/api/mat_kernel.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+
+#include "common.h"
+
+using GemmFn = void (*)(const KERNEL_CBLAS_LAYOUT layout, const KERNEL_CBLAS_TRANSPOSE transa,
+                        const KERNEL_CBLAS_TRANSPOSE transb, const KERNEL_CBLAS_OFFSET offsetc, const size_t m,
+                        const size_t n, const size_t k, const float alpha, const void* a, const size_t lda,
+                        const int8_t oa, const void* b, const size_t ldb, const int8_t ob, const float beta, int32_t* c,
+                        const size_t ldc, const int32_t* oc);
+
+struct MatKernelSelection {
+  GemmFn fn;
+  int divide_elements_size;
+};
+
+MatKernelSelection select_kernel_for_int4(MatKernelVariant variant);
+MatKernelSelection select_kernel_for_int8(MatKernelVariant variant);
+
+template <typename T>
+MatKernelSelection select_mat_kernel(MatKernelVariant variant) {
+  if constexpr (std::is_same_v<typename T::dt, int4_2_t>) {
+    return select_kernel_for_int4(variant);
+  } else {
+    return select_kernel_for_int8(variant);
+  }
+}