mesh.hex.blocks: one conforming hex mesh of a design split into blocks

Meshes the open design's bodies (or the listed ones) as the cells of one
conforming all-hex mesh with one size and tessellation tolerance for all;
elements carry their cell's body, boundary faces its B-rep faces. A cell
that is no block, or cells that touch without sharing whole faces, is an
error naming the bodies. Catalogue entry with its VectorCraft icon, the
MCP mesh tool's hex_blocks method, docs/features.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/Cargo.toml

@@ -27,3 +27,5 @@ log = { workspace = true }
 
 [dev-dependencies]
 zip = { workspace = true }
+# Multi-body designs from SolidCraft scripts in tests.
+fieldcraft-geometry = { workspace = true, features = ["scripts"] }