Fix latent memory error exposed by fixed_hierarchy_test (#668)

A weakness in GCC 15.1 was exposed when unwinding the stack due to an exception throw.

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Co-authored-by: Beojan Stanislaus <beojan@gmail.com>

Author: knoepfel

phlex/model/fixed_hierarchy.cpp

@@ -52,14 +52,15 @@ namespace {
     std::vector<std::vector<std::string>>&& layer_path_strings)
   {
     using namespace phlex::experimental;
-    auto layer_paths =
-      std::move(layer_path_strings) | std::views::transform([](std::vector<std::string>& lp) {
-        auto lp_as_ids =
-          lp | std::views::transform([](auto& str) { return identifier(std::move(str)); }) |
-          std::ranges::to<std::vector>();
-        return layer_path(std::move(lp_as_ids));
-      }) |
-      std::ranges::to<std::vector<layer_path>>();
+    std::vector<layer_path> layer_paths;
+    layer_paths.reserve(layer_path_strings.size());
+    for (auto& lp : layer_path_strings) {
+      auto lp_as_ids =
+        lp | std::views::as_rvalue |
+        std::views::transform([](std::string&& str) { return identifier(std::move(str)); }) |
+        std::ranges::to<std::vector>();
+      layer_paths.emplace_back(std::move(lp_as_ids));
+    }
     return unique_paths(std::move(layer_paths));
   }
 }