Use 30 max digits by default

This makes calculations much faster, and we may be more likely to find edge cases around the 64 bit limit.

random-tests.php

@@ -11,7 +11,7 @@
 
 use Brick\Math\Internal\Calculator;
 
-(new class(100) {
+(new class(30) { // max digits
     private $gmp;
     private $bcmath;
     private $native;