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/mesh/parallel_mc.h

@@ -0,0 +1,63 @@
+#pragma once
+/**
+ * @file parallel_mc.h
+ * @brief 并行 Marching Cubes
+ *
+ * 体素网格分块并行处理，每线程独立三角形缓冲区，最终合并。
+ * 支持自适应八叉树分辨率。
+ *
+ * @ingroup mesh
+ */
+
+#include "vde/mesh/halfedge_mesh.h"
+#include "vde/sdf/sdf_tree.h"
+#include <vector>
+#include <functional>
+
+namespace vde::mesh {
+
+// ═══════════════════════════════════════════════════════════
+//  Parallel Marching Cubes
+// ═══════════════════════════════════════════════════════════
+
+/// 并行 MC 配置
+struct ParallelMCConfig {
+    int resolution = 64;            ///< 基础分辨率（每轴体素数）
+    int num_threads = 0;            ///< 线程数（0 = 自动）
+    bool adaptive = false;          ///< 是否启用自适应分辨率
+    double min_voxel_size = 0.01;   ///< 自适应最小体素
+    int max_depth = 4;              ///< 自适应最大细分深度
+};
+
+/**
+ * @brief 并行 Marching Cubes
+ *
+ * 将体素网格沿 Z 轴分块，每线程处理一块。
+ * SDF 求值需要线程安全（只读操作）。
+ *
+ * @param sdf SDF 求值函数 f(x,y,z) → signed distance
+ * @param bounds 体素空间包围盒
+ * @param config 配置参数
+ * @return 生成的三角网格
+ */
+[[nodiscard]] HalfedgeMesh parallel_marching_cubes(
+    const std::function<double(double, double, double)>& sdf,
+    const core::AABB3D& bounds,
+    const ParallelMCConfig& config = {});
+
+/**
+ * @brief 并行自适应 Marching Cubes
+ *
+ * 平坦区域用大格子，曲面附近细分。
+ *
+ * @param sdf SDF 求值函数
+ * @param bounds 包围盒
+ * @param config 配置参数
+ * @return 生成的三角网格
+ */
+[[nodiscard]] HalfedgeMesh parallel_adaptive_mc(
+    const std::function<double(double, double, double)>& sdf,
+    const core::AABB3D& bounds,
+    const ParallelMCConfig& config = {});
+
+} // namespace vde::mesh