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

tests/core/test_exact_predicates.cpp

@@ -0,0 +1,73 @@
+#include <gtest/gtest.h>
+#include "vde/core/exact_predicates.h"
+#include <vector>
+#include <cmath>
+
+using namespace vde::core;
+
+TEST(ExactPredicatesTest, Orient2D_CounterClockwise) {
+    double r = exact_orient2d(0, 0, 1, 0, 0, 1);
+    EXPECT_GT(r, 0.0); // CCW
+}
+
+TEST(ExactPredicatesTest, Orient2D_Clockwise) {
+    double r = exact_orient2d(0, 0, 0, 1, 1, 0);
+    EXPECT_LT(r, 0.0);
+}
+
+TEST(ExactPredicatesTest, Orient2D_Collinear) {
+    double r = exact_orient2d(0, 0, 1, 1, 2, 2);
+    EXPECT_NEAR(r, 0.0, 1e-9);
+}
+
+TEST(ExactPredicatesTest, Orient3D_Above) {
+    // Tetrahedron: base on z=0, apex at z=1 → positive volume
+    double r = exact_orient3d(0,0,0, 1,0,0, 0,1,0, 0,0,1);
+    EXPECT_GT(r, 0.0);
+}
+
+TEST(ExactPredicatesTest, Orient3D_Coplanar) {
+    double r = exact_orient3d(0,0,0, 1,0,0, 0,1,0, 0.5,0.5,0);
+    EXPECT_NEAR(r, 0.0, 1e-9);
+}
+
+TEST(ExactPredicatesTest, InSphere_Inside) {
+    // Regular tetrahedron, point at centroid → inside circumsphere
+    double r = exact_in_sphere(0,0,0, 2,0,0, 0,2,0, 0,0,2, 0.2,0.2,0.2);
+    EXPECT_GT(r, 0.0);
+}
+
+TEST(ExactPredicatesTest, InSphere_OnSurface) {
+    double r = exact_in_sphere(0,0,0, 3,0,0, 0,3,0, 0,0,3, 0,0,3);
+    EXPECT_NEAR(r, 0.0, 1e-8);
+}
+
+TEST(ExactPredicatesTest, PointInPolygon_Inside) {
+    std::vector<Point3D> poly = {{0,0,0},{2,0,0},{2,2,0},{0,2,0}};
+    EXPECT_TRUE(exact_point_in_polygon({1,1,0}, poly));
+}
+
+TEST(ExactPredicatesTest, PointInPolygon_Outside) {
+    std::vector<Point3D> poly = {{0,0,0},{2,0,0},{2,2,0},{0,2,0}};
+    EXPECT_FALSE(exact_point_in_polygon({3,3,0}, poly));
+}
+
+TEST(ExactPredicatesTest, PointInPolygon_OnEdge) {
+    std::vector<Point3D> poly = {{0,0,0},{2,0,0},{2,2,0},{0,2,0}};
+    EXPECT_TRUE(exact_point_in_polygon({1,0,0}, poly));
+}
+
+TEST(ExactPredicatesTest, PrecisionMode) {
+    set_precision_mode(PrecisionMode::Fast);
+    EXPECT_EQ(precision_mode(), PrecisionMode::Fast);
+
+    set_precision_mode(PrecisionMode::Adaptive);
+    EXPECT_EQ(precision_mode(), PrecisionMode::Adaptive);
+
+    set_precision_mode(PrecisionMode::Adaptive); // restore default
+}
+
+TEST(ExactPredicatesTest, IsUncertain) {
+    EXPECT_TRUE(is_uncertain(1e-12));
+    EXPECT_FALSE(is_uncertain(1.0));
+}