ref(EX): import upstream ILU kernels + xllm MoE CUDA sources into ex_engine

Copied from upstream_ref (NOT rewritten — exact upstream code):

ixformer C++ API (the authoritative header):
  include/ixformer.h — ixformer::infer namespace: topk_softmax,
    moe_compute_token_index_api, moe_w16a16_group_gemm, moe_expand_input,
    moe_output_reduce_sum, silu_and_mul, rms_norm, xllm_paged_attention, etc.
  include/ilu_ops_api.h — xllm::kernel::ilu namespace: moe_active_topk,
    moe_gen_idx, moe_expand_input, group_gemm, moe_combine_result,
    batch_prefill, batch_decode, rms_norm, matmul, act_and_mul, etc.

ILU kernel wrappers (call ixformer::infer directly):
  csrc/ilu_kernel_fused_moe.cpp — topk routing + gen_idx + expand + combine
  csrc/ilu_kernel_group_gemm.cpp — batched expert GEMM
  csrc/ilu_kernel_{activation,norm,rope,matmul,attention}.cpp

ILU layer implementations (full pipeline):
  csrc/ilu_layer_fused_moe.{cpp,h} — 797 lines, the complete MoE pipeline
    that competitor 168 ran as corex_moe.py
  csrc/ilu_layer_attention.{cpp,h} — prefill/decode attention dispatch

CUDA MoE kernels (from xllm + ds_vllm):
  csrc/moe/moe_topk_softmax_kernels.cuh — CUB BlockReduce + warp topk
  csrc/moe/moe_topk_sigmoid_kernels.cuh — sigmoid scoring variant
  csrc/moe/moe_topk.cuh + moe_fused_topk.cu — entry points
  csrc/moe/moeTopKFuncs.cuh — TRT-LLM derived vllm-compatible topk
  csrc/moe/moe_ops.h + moe_align_sum_kernels.cu — alignment kernels

Common layer headers:
  csrc/common_fused_moe{,_base}.h + common_moe_fused_topk.{cpp,h}

ex_engine/include/ilu_utils.h

@@ -0,0 +1,63 @@
+/* Copyright 2025 The xLLM Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    https://github.com/jd-opensource/xllm/blob/main/LICENSE
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#pragma once
+namespace xllm::kernel::ilu {
+#undef check_tensor_contiguous
+#define check_tensor_contiguous(x, type) \
+  TORCH_CHECK(x.scalar_type() == type);  \
+  TORCH_CHECK(x.is_cuda());              \
+  TORCH_CHECK(x.is_contiguous());
+
+#undef check_tensor_half_bf_float
+#define check_tensor_half_bf_float(x)                       \
+  TORCH_CHECK(x.scalar_type() == at::ScalarType::Half ||    \
+              x.scalar_type() == at::ScalarType::Float ||   \
+              x.scalar_type() == at::ScalarType::BFloat16); \
+  TORCH_CHECK(x.is_cuda());
+
+// from torchCheckMsgImpl
+inline const char* ixformer_check_msg_impl(const char* msg) { return msg; }
+// // If there is just 1 user-provided C-string argument, use it.
+
+#define IXFORMER_CHECK_MSG(cond, type, ...)                 \
+  (ixformer_check_msg_impl(                                 \
+      "Expected " #cond                                     \
+      " to be true, but got false.  "                       \
+      "(Could this error message be improved?  If so, "     \
+      "please report an enhancement request to ixformer.)", \
+      ##__VA_ARGS__))
+
+#define IXFORMER_CHECK(cond, ...)                                            \
+  {                                                                          \
+    if (!(cond)) {                                                           \
+      std::cerr << __FILE__ << " (" << __LINE__ << ")"                       \
+                << "-" << __FUNCTION__ << " : "                              \
+                << IXFORMER_CHECK_MSG(cond, "", ##__VA_ARGS__) << std::endl; \
+      throw std::runtime_error("IXFORMER_CHECK ERROR");                      \
+    }                                                                        \
+  }
+
+#undef CUINFER_CHECK
+#define CUINFER_CHECK(func)                                                \
+  do {                                                                     \
+    cuinferStatus_t status = (func);                                       \
+    if (status != CUINFER_STATUS_SUCCESS) {                                \
+      std::cerr << "Error in file " << __FILE__ << " on line " << __LINE__ \
+                << ": " << cuinferGetErrorString(status) << std::endl;     \
+      throw std::runtime_error("CUINFER_CHECK ERROR");                     \
+    }                                                                      \
+  } while (0)
+
+}  // namespace xllm::kernel::ilu