Optimize Math.average with unchecked math (#6019)

Co-authored-by: Ernesto García <[email protected]>

Author: ZumZoom

contracts/utils/math/Math.sol

@@ -168,8 +168,10 @@ library Math {
      * zero.
      */
     function average(uint256 a, uint256 b) internal pure returns (uint256) {
-        // (a + b) / 2 can overflow.
-        return (a & b) + (a ^ b) / 2;
+        unchecked {
+            // (a + b) / 2 can overflow.
+            return (a & b) + (a ^ b) / 2;
+        }
     }
 
     /**