boost 1.91 rewrote boost::optional and made its converting constructor
unconditionally explicit, breaking aggregate brace-init of the radius
member in the profile_point structs. std::optional (C++17) keeps the
non-explicit converting constructor, so call sites compile unchanged.

--- a/src/ifcgeom/profile_helper.h
+++ b/src/ifcgeom/profile_helper.h
@@ -1,6 +1,8 @@
 #ifndef PROFILE_HELPER_H
 #define PROFILE_HELPER_H
 
+#include <optional>
+
 #include "taxonomy.h"
 
 namespace ifcopenshell {
@@ -8,18 +10,18 @@
 	namespace geometry {
 		struct profile_point {
 			std::array<double, 2> xy;
-			boost::optional<double> radius;
+			std::optional<double> radius;
 		};
 
 		struct profile_point_with_edges {
 			Eigen::Vector2d xy;
-			boost::optional<double> radius;
+			std::optional<double> radius;
 			taxonomy::edge::ptr previous, next;
 		};
 
 		struct profile_point_with_edges_3d {
 			Eigen::Vector3d xy;
-			boost::optional<double> radius;
+			std::optional<double> radius;
 			taxonomy::edge::ptr previous, next;
 		};