perf(dossier): memoize champ.sections on dossier

app/models/champ.rb

@@ -81,18 +81,8 @@ class Champ < ApplicationRecord
     !private?
   end
 
-  def siblings
-    if parent
-      parent&.champs
-    elsif public?
-      dossier&.champs
-    else
-      dossier&.champs_private
-    end
-  end
-
   def sections
-    siblings&.filter(&:header_section?)
+    @sections ||= dossier.sections_for(self)
   end
 
   def mandatory_and_blank?

app/models/dossier.rb

@@ -1122,6 +1122,20 @@ class Dossier < ApplicationRecord
     termine_expired_to_delete.find_each(&:purge_discarded)
   end
 
+  def sections_for(champ)
+    @sections = Hash.new do |hash, parent|
+      case parent
+      when :public
+        hash[parent] = champs.filter(&:header_section?)
+      when :private
+        hash[parent] = champs_private.filter(&:header_section?)
+      else
+        hash[parent] = parent.champs.filter(&:header_section?)
+      end
+    end
+    @sections[champ.parent || (champ.public? ? :public : :private)]
+  end
+
   private
 
   def create_missing_traitemets