[board] Refactor ray BitBoard lookups

Rearrange the generated ray bitboards into a 2D grid by square and direction.
Use the Direction vector for lookup.

board/src/bitboard/bitboard.rs

@@ -36,6 +36,10 @@ impl BitBoard {
         FILES[file]
     }
 
+    pub fn ray(sq: Square, dir: Direction) -> BitBoard {
+        library().ray(sq, dir)
+    }
+
     moves_getter!(knight_moves);
     moves_getter!(bishop_moves);
     moves_getter!(rook_moves);