Display tessellation plans (1/4): planner with shared edge nodes (#802)

Adds TessPlan and the kernel planner (shared edge nodes, structured and Coons grids, constrained Delaunay for trimmed faces) behind Body::display_plan. Nothing drawn changes yet.

Refs #303

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/kernel/src/lib.rs

@@ -54,6 +54,7 @@ mod native;
 mod numbered;
 mod offset;
 mod ops;
+mod par;
 mod plane_fit;
 mod polybool;
 mod polyhedron;
@@ -72,6 +73,7 @@ mod step_out;
 mod surface_kind;
 mod surfaces;
 mod sweep_path;
+mod tess;
 #[cfg(test)]
 mod thread_tests;
 mod topo;