upstream(xllm): sync to jd-opensource/xllm latest + revert serving_chat.py

搬运 jd-opensource/xllm 最新代码到 upstream_ref/xllm_latest/:
- core/kernels/ilu/ 10 files (ixformer.h API 不变)
- core/layers/ilu/ 4 files (fused_moe.cpp config 访问从 FLAGS→singleton)
- core/layers/npu_torch/ 14 files (qwen3_gated_delta_net_base.cpp 576→1164行,
  新增 repeat_tensor_heads, checkpoint_stride, spec_verify 等 GDN 功能)
- models/llm/ 5 files (qwen3_5.h 模型注册重构, 新增 qwen3_5_mtp_base.h)
- models/vlm/ 1 file (qwen3_5.h 218→440行)

serving_chat.py: 还原到 8030a11b 原版,删掉 6dcf3590 的语法错误 min(8192,
(缺右括号导致 py_compile 失败)

qwen3_6_scripts/serving_chat.py

@@ -394,7 +394,7 @@ class OpenAIServingChat(OpenAIServing):
             assert prompt_inputs is not None
 
             sampling_params: Union[SamplingParams, BeamSearchParams]
-            default_max_tokens = min(8192, self.max_model_len - len(
+            default_max_tokens = self.max_model_len - len(
                 prompt_inputs["prompt_token_ids"])
             if request.use_beam_search:
                 sampling_params = request.to_beam_search_params(