split_faces: exact sketch segments, a face map, and misses named

For solvecraft-params' Split Face feature:
- Sketch tools are chains of Seg2. A single line splits by its plane and a
  single arc by its cylinder, exactly (a circular edge on a planar face);
  longer chains and splines follow the curve.
- split_faces_with_map gives the source face of each face of the result.
- A listed face the tool misses is an error naming it (split_any keeps
  the lenient form for Trim).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/kernel/src/lib.rs

@@ -53,7 +53,7 @@ pub use ops::{BoolOp, boolean, split_by_plane, transform, transform_matrix};
 pub use polybool::planar_boolean;
 pub use polyhedron::{HalfSpace, convex_polyhedron, draft, offset_faces, shell};
 pub use sew::{EdgeSpec, FaceSpec, SurfSpec, sew};
-pub use splitface::{SplitTool, split_body, split_faces};
+pub use splitface::{SplitTool, split_body, split_faces, split_faces_with_map};
 pub use step::step_export;
 pub use step_in::{ImportedBody, StepImport, StepNode, step_import, step_import_shared, step_orientation_errors, step_validate};
 pub use step_out::{ExportBody, ExportProduct, StepHeader, step_export_bodies, step_export_products};