feat: add keep_highest method to Outcome

01.workspace/oxidice_lib/examples/roll_exploding_d6.rs

@@ -1,6 +1,6 @@
 use oxidice_lib::dice::*;
 
-fn main(){
+fn main() {
     let roll = Handful::grab_exploding(1, 6, 6).roll();
     println!("{roll}");
 }