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/CadDocument.cpp

@@ -42,6 +42,10 @@
 #include <cmath>
 #include <stdexcept>
 #include <algorithm>
+#include <sstream>
+
+#include <cereal/archives/binary.hpp>
+#include <BRepTools.hxx>
 
 namespace Slic3r {
 
@@ -1537,4 +1541,52 @@ bool CadDocument::preview(const CadFeature& candidate, TriangleMesh& out_mesh, s
     return preview(candidate, out_mesh, ignore, err);
 }
 
+std::string brep_to_string(const TopoDS_Shape& s)
+{
+    if (s.IsNull()) return {};
+    std::ostringstream oss;
+    BRepTools::Write(s, oss);
+    return oss.str();
+}
+
+TopoDS_Shape brep_from_string(const std::string& d)
+{
+    if (d.empty()) return {};
+    std::istringstream iss(d);
+    TopoDS_Shape s;
+    BRep_Builder b;
+    BRepTools::Read(s, iss, b);
+    return s;
+}
+
+std::string CadDocument::serialize_recipe() const
+{
+    std::ostringstream oss;
+    {
+        cereal::BinaryOutputArchive ar(oss);
+        uint32_t v = SNAPORCA_CAD_RECIPE_VERSION;
+        ar(v);
+        ar(features);
+    }
+    return oss.str();
+}
+
+bool CadDocument::deserialize_recipe(const std::string& blob)
+{
+    try {
+        std::istringstream iss(blob);
+        cereal::BinaryInputArchive ar(iss);
+        uint32_t v;
+        ar(v);
+        if (v > SNAPORCA_CAD_RECIPE_VERSION)
+            return false;
+        ar(features);
+        return recompute();
+    } catch (const Standard_Failure&) {
+        return false;
+    } catch (...) {
+        return false;
+    }
+}
+
 } // namespace Slic3r