only fetch ratings once when suggesting a game

lib/rank_king.rb

@@ -5,14 +5,17 @@ module RankKing
   OS = OpenSkill.new
   Match = Data.define(:a, :b)
 
+  # rates all possible 1v1 games to find which generally decreases sigma
+  # regardless of the winner/loser - is this mathematically sound? I have
+  # no idea
   def self.suggest_game(axis)
     items = axis.pool.items
+    ratings = items.to_h { [_1.id, Rating.first(axis:, item: _1) || OS.rating] }
 
     items.combination(2).sort_by {|combo|
-      # TODO get all the ratings at once
-      ratings = combo.map {|item| Rating.first(axis:, item:) || OS.rating }
+      game = combo.map { ratings.fetch(_1.id) }
       Math.sqrt(
-        [ratings, ratings.reverse]
+        [game, game.reverse]
           .map {|game| [game, OS.rate(*game).flatten] }
           .sum {|pre,post| pre.zip(post).sum { (_1.sigma - _2.sigma)**2 }}
       )