feat: add method max to Outcome

01.workspace/oxidice_lib/examples/roll_d20_with_advantage.rs

@@ -0,0 +1,7 @@
+use oxidice_lib::dice::*;
+
+fn main() {
+    let roll_result = Handful::grab(2, 20).roll();
+    let result = roll_result.clone().max().unwrap();
+    println!("{} -> {}", roll_result, result);
+}