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/cmake/CMakeDetermineRustCompiler.cmake

@@ -0,0 +1,25 @@
+# ported from https://github.com/Devolutions/CMakeRust
+if(NOT CMAKE_Rust_COMPILER)
+	find_package(Rust)
+	if(RUST_FOUND)
+		set(CMAKE_Rust_COMPILER "${RUSTC_EXECUTABLE}")
+		set(CMAKE_Rust_COMPILER_ID "Rust")
+		set(CMAKE_Rust_COMPILER_VERSION "${RUST_VERSION}")
+		set(CMAKE_Rust_PLATFORM_ID "Rust")
+	endif()
+endif()
+
+message(STATUS "Cargo Home: ${CARGO_HOME}")
+message(STATUS "Rust Compiler Version: ${RUSTC_VERSION}")
+
+mark_as_advanced(CMAKE_Rust_COMPILER)
+
+if(CMAKE_Rust_COMPILER)
+	set(CMAKE_Rust_COMPILER_LOADED 1)
+endif(CMAKE_Rust_COMPILER)
+
+configure_file(${CMAKE_CURRENT_LIST_DIR}/CMakeRustCompiler.cmake.in
+	${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/${CMAKE_VERSION}/CMakeRustCompiler.cmake IMMEDIATE @ONLY)
+
+set(CMAKE_Rust_COMPILER_ENV_VAR "RUSTC")
+