Geometry: partition a design's bodies by planes, with paired cut-face names

Design::partitioned cuts the bodies as opened by planes in order (SolidCraft's
split_by_plane, in memory). Cells are <body>/a and <body>/b by side of the plane;
the two faces of each cut are partition:<name>:a and :b, and every other face
inherits the name of the face it is a piece of (<name>#k when a cell holds
several pieces). A cut that misses or names an unknown body is reported as a
design error, not fatal.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/geometry/src/lib.rs

@@ -18,11 +18,13 @@
 #![forbid(unsafe_code)]
 
 mod design;
+pub mod partition;
 pub mod sample;
 #[cfg(feature = "scripts")]
 mod script;
 
 pub use design::{Design, FeatureError, MAX_DESIGN_BYTES, open_design};
+pub use partition::{Cut, CutReport};
 pub mod tagged_mesh;
 #[cfg(feature = "scripts")]
 pub use script::{MAX_SCRIPT_BYTES, script_design};