overhaul chain system

This made the code so fast, that the `board` benchmark became completely useless.
So that benchmark was removed.

Overall, we're looking at a futher 20% performance increase in `future_moves`

src/elo.rs

@@ -135,8 +135,8 @@ impl PlayerArena {
     }
 
     fn create_agents(
-        player_1_fn: &Box<dyn Fn(Piece) -> Box<dyn Agent>>,
-        player_2_fn: &Box<dyn Fn(Piece) -> Box<dyn Agent>>,
+        player_1_fn: &dyn Fn(Piece) -> Box<dyn Agent>,
+        player_2_fn: &dyn Fn(Piece) -> Box<dyn Agent>,
     ) -> (Box<dyn Agent>, Box<dyn Agent>) {
         (player_1_fn(Piece::Black), player_2_fn(Piece::White))
     }