ref(upstream): FULL TREE — Deep-Spark xllm (1470) + ds_vllm csrc/models (703)

Replaces cherry-picked upstream_ref with complete source trees.

xllm/ — Iluvatar official C++ inference engine (15MB, 1470 files)
  Complete: kernels → layers → models → runtime → scheduler → api
  Excluded: .git, binary images, third_party submodule checkouts

ds_vllm/ — Iluvatar official vllm fork (8MB, 703 files)
  Included: csrc/ (ALL CUDA kernels), fused_moe/, qwen3_5 model, _custom_ops
  Excluded: tests, benchmarks, docs, examples (not needed for reference)

Critical call chains now fully traceable:
  MoE: moe_topk_softmax_kernels.cuh → ixformer.h → fused_moe.cpp → layer
  GDN: qwen3_gated_delta_net_base.cpp → qwen3_5_gated_delta_net.cpp
  Attention: ixformer.h → xllm_paged_attention → attention.cpp

upstream_ref/xllm/docs/zh/features/continuous_scheduler.md

@@ -0,0 +1,7 @@
+# Continuous调度器
+
+## 功能介绍
+xLLM实现了支持continuous batching的调度策略，continuous_batch是一种动态批处理策略，它不等待批次填满，而是在有请求时就开始处理，同时持续接收新请求并将其加入正在执行的批次中，从而在保持高吞吐量的同时显著降低延迟。
+
+## 使用方式
+xLLM提供了continuous batching调度策略。目前`enable_chunked_prefill`默认值为true，开箱即用时默认调度器是chunked prefill调度器。