use a non-recursive algorithm for sort_by_ancestry

lib/ancestry/class_methods.rb

@@ -68,12 +68,24 @@ def arrange_nodes(nodes)
     # @param arranged [Hash{Node => {Node => {}, Node => {}}}] arranged nodes
     # @returns [Array[Node]] array of nodes with the parent before the children
     def flatten_arranged_nodes(arranged)
-      arranged.inject([]) do |sorted_nodes, pair|
-        node, children = pair
-        sorted_nodes << node
-        sorted_nodes += flatten_arranged_nodes(children) unless children.blank?
-        sorted_nodes
+      nodes = []
+      stack = []
+      cur = arranged
+      while cur.present? || stack.present?
+        node, children = cur.first
+        nodes << node
+        children = cur.delete(node)
+
+        if children.present?
+          # work on children, will continue on current node later
+          stack.push(cur) if cur.present?
+          cur = children
+        elsif cur.empty?
+          # return to remembered node if done processing current children
+          cur = stack.pop
+        end
       end
+      nodes
     end
 
      # Arrangement to nested array for serialization