[C][PyTorch] Move multi tensors kernels from PyTorch extensions to core (#1744)

* Move multi tensors kernels from PyTorch extensions to core
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Add int16 type to core (for storing fp32 param remainders)
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix core build
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* same fix to scale
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix perf, memory, vars
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Re-add device guard for multi-device
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix junk output dtype for non-per tensor
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fixes for test and upgrade mcore version
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

* Fix core tests
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

---------
Signed-off-by: Kirthi Shankar Sivamani <ksivamani@nvidia.com>

transformer_engine/pytorch/csrc/extensions/multi_tensor/scale.cpp

+/*************************************************************************
+ * Copyright (c) 2022-2025, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ *
+ * See LICENSE for license information.
+ ************************************************************************/
+
+#include "extensions.h"
+
+void multi_tensor_scale_cuda(int chunk_size, at::Tensor noop_flag,
+                             std::vector<std::vector<at::Tensor>> tensor_lists, float scale) {
+  using namespace transformer_engine;
+  using namespace transformer_engine::pytorch;
+
+  auto noop_flag_cu = makeTransformerEngineTensor(noop_flag);
+  auto [_, __, tensor_lists_ptr, num_lists, num_tensors] =
+      makeTransformerEngineTensorList(tensor_lists);
+  int device_id = tensor_lists[0][0].device().index();
+
+  nvte_multi_tensor_scale_cuda(chunk_size, noop_flag_cu.data(), tensor_lists_ptr.data(), num_lists,
+                               num_tensors, scale, device_id, at::cuda::getCurrentCUDAStream());
+}

transformer_engine/pytorch/csrc/extensions/multi_tensor/sgd.cpp

+/*************************************************************************
+ * Copyright (c) 2022-2025, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ *
+ * See LICENSE for license information.
+ ************************************************************************/
+
+#include "extensions.h"
+
+void multi_tensor_sgd_cuda(int chunk_size, at::Tensor noop_flag,
+                           std::vector<std::vector<at::Tensor>> tensor_lists, float wd,
+                           float momentum, float dampening, float lr, bool nesterov, bool first_run,
+                           bool wd_after_momentum, float scale) {
+  using namespace transformer_engine;
+  using namespace transformer_engine::pytorch;
+
+  auto noop_flag_cu = makeTransformerEngineTensor(noop_flag);
+  auto [_, __, tensor_lists_ptr, num_lists, num_tensors] =
+      makeTransformerEngineTensorList(tensor_lists);
+  int device_id = tensor_lists[0][0].device().index();
+
+  nvte_multi_tensor_sgd_cuda(chunk_size, noop_flag_cu.data(), tensor_lists_ptr.data(), num_lists,
+                             num_tensors, wd, momentum, dampening, lr, nesterov, first_run,
+                             wd_after_momentum, scale, device_id, at::cuda::getCurrentCUDAStream());
+}