Fix #8050: clone mapped items before in place mutation in geometry mapping

The mapping cache returns the same shared taxonomy item on a hit, so
mutating a map() result corrupts the cached item that other
representations reuse. Under multithreading this produced nondeterministic
geometry. Clone before mutating at every site that writes into a map()
result, matching the existing idiom in IfcOrientedEdge, IfcDerivedProfileDef
and IfcArbitraryOpenProfileDef. This fixes the race at the mutation site and
keeps the mapping cache enabled.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ifcgeom/mapping/IfcCompositeCurve.cpp

@@ -53,6 +53,9 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcCompositeCurve* inst) {
 			auto crv = map(segment->as<IfcSchema::IfcCompositeCurveSegment>()->ParentCurve());
 			if (crv) {
 				if (!segment->as<IfcSchema::IfcCompositeCurveSegment>()->SameSense()) {
+					// Clone before reversing so we do not corrupt the shared cached
+					// curve that map() may return for other segments.
+					crv.reset(crv->clone_());
 					crv->reverse();
 				}
 				if (crv->kind() == taxonomy::EDGE) {

src/ifcgeom/mapping/IfcEdge.cpp

@@ -43,6 +43,9 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcEdge* inst) {
 		auto basis = map(inst->as<IfcSchema::IfcEdgeCurve>()->EdgeGeometry());
 		auto loop = taxonomy::dcast<taxonomy::loop>(basis);
 		if (loop && loop->children.size() == 1) {
+			// Clone before mutating so calculate_linear_edge_curves does not write
+			// into the child edges of the shared cached loop returned by map().
+			loop.reset(loop->clone_());
 			loop->calculate_linear_edge_curves();
 			basis = loop->children[0]->basis;
 		}

src/ifcgeom/mapping/IfcFace.cpp

@@ -26,18 +26,14 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcFace* inst) {
 	auto bounds = inst->Bounds();
 	for (auto& bound : *bounds) {
 		if (auto r = taxonomy::cast<taxonomy::loop>(map(bound->Bound()))) {
+			// Clone before mutating so we do not corrupt the shared cached loop
+			// that map() may return for other faces referencing the same bound.
+			r.reset(r->clone_());
 			if (!bound->Orientation()) {
 				r->reverse();
 			}
 			// @todo check why loop sets external to true initially
 			r->external = bound->declaration().is(IfcSchema::IfcFaceOuterBound::Class());
-			/*
-			// Make a copy in case we need immutability later for e.g. caching
-			auto s = r->clone();
-			((taxonomy::loop*)s)->external = true;
-			delete r;
-			r = s;
-			*/
 			face->children.push_back(r);
 		}
 	}