Mirror CAD persistence (K1+K2+G1) from snaporca-cad onto mainline OrcaSlicer

Dual-fork mandate: port the parametric-recipe 3MF persistence from
snaporca-cad commits ed19eac+147e1c4 so a saved project reopens with the
editable CAD feature tree, not just the baked mesh.

Shared kernel/format/GUI (identical to snaporca-cad):
- CadDocument serialize_recipe/deserialize_recipe (cereal BinaryArchive,
  versioned) + CadFeature split save/load + imported_solid<->BRep string.
- Model::cad_recipe carried through 3MF zip entry Metadata/SnapOrca_cad.bin
  (writer + binary-verbatim reader branch).
- DesignPanel on_commit() stamps the recipe; on_tab_shown() rehydrates a
  loaded project via load_recipe() (deserialize -> feed_bodies + refresh_tree).

Mainline-only adapters (no snaporca-cad counterpart — Catch2 v3 vs v2):
- tests/libslic3r/test_caddocument.cpp: <catch2/catch_all.hpp> +
  `using Catch::Approx;` (v3 scopes Approx under Catch::).
- tests/libslic3r/CMakeLists.txt: register test_caddocument.cpp (the
  original CAD port had left it out of the test build).

Verified on behemoth (snaporca-deps toolchain): libslic3r_tests clean;
[CadDocument] 17/18 (only the pre-existing tangent-to-circle SIGABRT fails,
identical to snaporca-tkz); K1 serialize round-trip + version-reject pass
(13 assertions); new [3mf] "CAD recipe blob survives a 3mf save/load cycle"
passes byte-for-byte; orca-slicer GUI links clean (186/186, DesignPanel.cpp
compiled). Interactive :10 click-through pending (no Design-tab automation).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVzKmX6Y1aEteit1HTXG4Q

src/libslic3r/Model.cpp

@@ -105,6 +105,8 @@ Model& Model::assign_copy(const Model &rhs)
     this->md_name = rhs.md_name;
     this->md_value = rhs.md_value;
 
+    this->cad_recipe = rhs.cad_recipe;
+
     return *this;
 }
 
@@ -148,6 +150,7 @@ Model& Model::assign_copy(Model &&rhs)
     rhs.model_info.reset();
     this->profile_info = rhs.profile_info;
     rhs.profile_info.reset();
+    this->cad_recipe = std::move(rhs.cad_recipe);
     return *this;
 }