feat: 添加Math库和Google Test测试框架

- 新增Math库: Vector2/3/4, Matrix3/4, Quaternion, Transform, Color等
- 新增测试框架: Google Test (gtest)
- 新增140个单元测试，覆盖Vector, Matrix, Quaternion, Geometry
- VolumeRenderer支持vcpkg的NanoVDB
- 添加TESTING.md测试文档

engine/CMakeLists.txt

@@ -0,0 +1,43 @@
+cmake_minimum_required(VERSION 3.15)
+project(XCEngine)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+add_library(XCEngine STATIC
+    include/XCEngine/Math/Math.h
+    include/XCEngine/Math/Vector2.h
+    include/XCEngine/Math/Vector3.h
+    include/XCEngine/Math/Vector4.h
+    include/XCEngine/Math/Matrix3.h
+    include/XCEngine/Math/Matrix4.h
+    include/XCEngine/Math/Quaternion.h
+    include/XCEngine/Math/Transform.h
+    include/XCEngine/Math/Color.h
+    include/XCEngine/Math/Ray.h
+    include/XCEngine/Math/Plane.h
+    include/XCEngine/Math/Sphere.h
+    include/XCEngine/Math/Box.h
+    include/XCEngine/Math/Bounds.h
+    include/XCEngine/Math/Frustum.h
+    include/XCEngine/Math/Rect.h
+    include/XCEngine/Math/AABB.h
+    src/Math/Matrix.cpp
+    src/Math/Quaternion.cpp
+    src/Math/Transform.cpp
+    src/Math/Color.cpp
+    src/Math/Geometry.cpp
+    src/Math/FrustumBounds.cpp
+)
+
+target_include_directories(XCEngine PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine
+    ${CMAKE_CURRENT_SOURCE_DIR}/src
+)
+
+if(MSVC)
+    target_compile_options(XCEngine PRIVATE /W3)
+else()
+    target_compile_options(XCEngine PRIVATE -Wall)
+endif()