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/csrc/common_moe_fused_topk.h

@@ -0,0 +1,53 @@
+/* Copyright 2026 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
+
+#include <torch/torch.h>
+
+#include "framework/model/model_args.h"
+#include "framework/quant_args.h"
+#include "framework/state_dict/state_dict.h"
+#include "framework/state_dict/utils.h"
+
+namespace xllm {
+namespace layer {
+
+class MoEFusedTopkImpl : public torch::nn::Module {
+ public:
+  MoEFusedTopkImpl(const ModelArgs& model_args,
+                   const QuantArgs& quant_args,
+                   const torch::TensorOptions& options);
+
+  std::tuple<torch::Tensor, torch::Tensor> forward(
+      torch::Tensor& router_logits);
+
+  void load_state_dict(const StateDict& state_dict);
+
+ private:
+  int64_t topk_;
+  int64_t num_expert_group_;
+  int64_t topk_group_;
+  double route_scale_;
+  int64_t hidden_size_;
+  bool renormalize_;
+  std::string scoring_func_;
+
+  DEFINE_WEIGHT(e_score_correction_bias);
+};
+
+TORCH_MODULE(MoEFusedTopk);
+}  // namespace layer
+}  // namespace xllm