fix(critical): fold max_completion_tokens + max_num_seqs=2 + max_model_len=80000 + xllm_latest layer import

Sub 655 root causes (confirmed from log analysis):
1. protocol.py: max_completion_tokens never folded into max_tokens
   → 162/881 replay requests rejected 400 (extra_forbidden)
2. max_num_seqs=1 → t2_n_2 test fails (needs n=2)
3. max_model_len=131072 → OOM crash at 62% replay, opencompass all 0

Fixes:
- protocol.py: model_validator fold_max_completion_tokens
- yaml: max_num_seqs=2, max_model_len=80000, PYTORCH_CUDA_ALLOC_CONF
- topk_softmax stays =0 (corex CUB BlockReduce incompatible on BI-V100)

xllm_latest import to ex_engine/:
- npu_torch layers: GDN(1164L), Qwen3.5 GDN, attention, fused_moe
- cuda/moe kernels: topk_softmax_kernels.cuh, moe_combine, moe_compute_index
- npu kernels: causal_conv1d, recurrent_gated_delta_rule
- model headers: qwen3_5.h, qwen3_next.h

ex_engine/csrc/ilu_CMakeLists.txt

@@ -0,0 +1,28 @@
+include(cc_library)
+set(CMAKE_CUDA_ARCHITECTURES ivcore11)
+file(GLOB_RECURSE ILU_HEADER_FILES
+  "${CMAKE_CURRENT_LIST_DIR}/*.h"
+)
+
+file(GLOB_RECURSE ILU_SOURCE_FILES
+  "${CMAKE_CURRENT_LIST_DIR}/*.cpp"
+  "${CMAKE_CURRENT_LIST_DIR}/*.cu"
+)
+
+find_package(Python3 REQUIRED COMPONENTS Interpreter Development)
+
+cc_library(
+  NAME
+    ilu_kernels
+  HDRS
+    ${ILU_HEADER_FILES}
+  SRCS
+    ${ILU_SOURCE_FILES}
+  DEPS
+    torch
+    :util
+    ixformer_kernels
+    ixformer
+    ${Python3_LIBRARIES}
+    cuinfer
+)

ex_engine/csrc/ilu_layers_CMakeLists.txt

@@ -0,0 +1,14 @@
+include(cc_library)
+
+cc_library(
+  NAME
+    ilu_layers
+  HDRS
+    attention.h
+    fused_moe.h
+  SRCS
+    attention.cpp
+    fused_moe.cpp
+  DEPS
+    :common_layers
+)