fix: contact and shell-grouping checks use a shared broad phase (#838)

Contact and shell-grouping checks find close triangle pairs through one shared grid instead of testing every pair. Refs #232.

crates/geom/src/lib.rs

@@ -21,7 +21,7 @@ pub mod tspline;
 mod vec;
 
 pub use arcfit::MAX_FIT_PIECES;
-pub use mesh::{Aabb3, InsideIndex, Mesh, MeshMeasure};
+pub use mesh::{Aabb3, BoxedTriangle, InsideIndex, Mesh, MeshMeasure, find_close_pair};
 pub use plane::Plane;
 pub use profile::{Loop2, MAX_BEZIER_DEGREE, Region2, Seg2, bezier};
 pub use vec::{Vec2, Vec3};