Day03: Minor simplification

While neat, it does not make sense to do all this list allocation just to get two regexp groups in a neat way.

lib/day03.dart

@@ -6,8 +6,7 @@ int solveA(Iterable<String> input) {
   var sum = 0;
 
   for (final match in input.expand(regExp.allMatches)) {
-    final [arg1!, arg2!] = match.groups([1, 2]);
-    sum += int.parse(arg1) * int.parse(arg2);
+    sum += int.parse(match[1]!) * int.parse(match[2]!);
   }
 
   return sum;
@@ -24,8 +23,7 @@ int solveB(Iterable<String> input) {
     } else if (match[0] == "don't()") {
       mulEnabled = false;
     } else if (mulEnabled) {
-      final [arg1!, arg2!] = match.groups([1, 2]);
-      sum += int.parse(arg1) * int.parse(arg2);
+      sum += int.parse(match[1]!) * int.parse(match[2]!);
     }
   }