feat(v4.6): memory pool + parallel boolean/MC/intersection + GMP exact predicates

M1 — Memory Pool (内存池):
- ObjectPool<T>: O(1) acquire/release with free-list, chunk-based expansion
- ThreadSafeObjectPool<T>: per-thread local pools with global fallback
- CowPtr<T>: copy-on-write smart pointer with shallow/deep copy
- 10 tests: single/multi-thread, CoW detach, reuse rate

M2 — Parallel Boolean (并行布尔):
- parallel_face_face_intersection(): OpenMP face-pair dispatch with AABB culling
- parallel_classify_faces(): thread-safe ray casting classification
- parallel_mesh_union/intersection/difference + B-Rep variants
- Thread count management API
- 12 tests: coverage, empty cases, identity operations

M3 — Parallel Marching Cubes (并行MC):
- parallel_marching_cubes(): Z-slice parallel voxel processing
- parallel_adaptive_mc(): octree-based adaptive resolution
- Complete 256-entry edge table + Möller-Trumbore interpolation
- 5 tests: sphere basic/high-res/empty/adaptive/threaded

M4 — Parallel Surface Intersection (并行求交):
- parallel_curve_intersections(): per-pair parallel dispatch
- parallel_surface_intersection(): recursive subdivision + Newton refinement
- AABB broad-phase culling before narrow-phase
- 4 tests: curve pairs, surface batch

M5 — GMP Exact Predicates (精确谓词):
- exact_orient2d/3d: adaptive precision (double → GMP fallback)
- exact_in_sphere: circumsphere test with degenerate handling
- exact_point_in_polygon/polyhedron: robust ray casting
- PrecisionMode: Fast/Adaptive/Exact with global toggle
- 12 tests: all orientations, boundary cases, mode switching

21 files, +2263 lines

include/vde/core/exact_predicates.h

@@ -0,0 +1,116 @@
+#pragma once
+/**
+ * @file exact_predicates.h
+ * @brief 精确几何谓词
+ *
+ * 使用 GMP/MPFR 进行精确算术运算，消除浮点误差。
+ * 关键路径：布尔运算分类、Delaunay 三角剖分、凸包计算。
+ *
+ * 支持混合精度：先用 double，检测到不确定时自动升级到 GMP。
+ *
+ * @ingroup foundation
+ */
+
+#include "vde/core/point.h"
+#include <vector>
+
+namespace vde::core {
+
+// ═══════════════════════════════════════════════════════════
+//  Exact Predicates (double → GMP fallback)
+// ═══════════════════════════════════════════════════════════
+
+/**
+ * @brief 精确三点定向 (orient2d)
+ *
+ * 计算 (ax,ay), (bx,by), (cx,cy) 的有向面积 × 2。
+ * > 0 → 逆时针, < 0 → 顺时针, = 0 → 共线。
+ *
+ * 先使用浮点运算，若结果接近 0 则升级到 GMP。
+ *
+ * @return 精确的 orient 值
+ */
+[[nodiscard]] double exact_orient2d(
+    double ax, double ay, double bx, double by, double cx, double cy);
+
+/**
+ * @brief 精确四点定向 (orient3d)
+ *
+ * 计算四面体 (a,b,c,d) 的有向体积 × 6。
+ * > 0 → d 在平面 abc 上方, < 0 → 下方, = 0 → 共面。
+ */
+[[nodiscard]] double exact_orient3d(
+    double ax, double ay, double az,
+    double bx, double by, double bz,
+    double cx, double cy, double cz,
+    double dx, double dy, double dz);
+
+/**
+ * @brief 精确球内测试 (in_sphere)
+ *
+ * 判断点 d 是否在四面体 abc 的外接球内。
+ * > 0 → 内部, < 0 → 外部, = 0 → 在球面上。
+ */
+[[nodiscard]] double exact_in_sphere(
+    double ax, double ay, double az,
+    double bx, double by, double bz,
+    double cx, double cy, double cz,
+    double dx, double dy, double dz,
+    double ex, double ey, double ez);
+
+/**
+ * @brief 精确点在多边形内测试
+ *
+ * 射线投射法 + 精确算术处理边界情况。
+ *
+ * @param point 测试点
+ * @param polygon 多边形顶点（逆时针）
+ * @return true 如果点在多边形内或边界上
+ */
+[[nodiscard]] bool exact_point_in_polygon(
+    const Point3D& point, const std::vector<Point3D>& polygon);
+
+/**
+ * @brief 精确点在多面体内测试
+ *
+ * 射线投射法，使用精确算术处理共面/共线退化情况。
+ *
+ * @param point 测试点
+ * @param vertices 多面体顶点
+ * @param faces 面索引（每面 3+ 个顶点索引）
+ * @return true 如果点在体内
+ */
+[[nodiscard]] bool exact_point_in_polyhedron(
+    const Point3D& point,
+    const std::vector<Point3D>& vertices,
+    const std::vector<std::vector<int>>& faces);
+
+// ═══════════════════════════════════════════════════════════
+//  Adaptive precision wrapper
+// ═══════════════════════════════════════════════════════════
+
+/// 精度模式
+enum class PrecisionMode {
+    Fast,     ///< 仅使用 double（默认）
+    Adaptive, ///< 先 double，不确定时升级到 GMP
+    Exact,    ///< 始终使用 GMP
+};
+
+/**
+ * @brief 设置全局精度模式
+ */
+void set_precision_mode(PrecisionMode mode);
+
+/**
+ * @brief 获取当前精度模式
+ */
+[[nodiscard]] PrecisionMode precision_mode();
+
+/**
+ * @brief 检查和报告两浮点数是否在误差范围内"不确定"
+ *
+ * 用于自适应精度升级判断。
+ */
+[[nodiscard]] bool is_uncertain(double value, double threshold = 1e-10);
+
+} // namespace vde::core