Add Prettier for linting and fix Solhint config (#2697)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/utils/math/Math.sol

@@ -26,7 +26,7 @@ library Math {
      */
     function average(uint256 a, uint256 b) internal pure returns (uint256) {
         // (a + b) / 2 can overflow, so we distribute.
-        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
+        return (a / 2) + (b / 2) + (((a % 2) + (b % 2)) / 2);
     }
 
     /**