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/surfaces.rs

@@ -463,7 +463,7 @@ pub fn trim(body: &Body, tool: &crate::SplitTool, keep: Vec3) -> Result<Body> {
     body.require_brep("trim")?;
     let total = body.solid.face_iter().count();
     let all: Vec<usize> = (0..total).collect();
-    let split = crate::split_faces(body, &all, tool)?;
+    let (split, _) = crate::splitface::split_any(body, &all, tool)?;
     let side = crate::splitface::side_of_point(tool, keep)?;
     guard("trim", || {
         let mut kept = Vec::new();