Switch to rust edition 2021.

src/tasks/day24.rs

@@ -228,7 +228,7 @@ impl Life {
                 if self.at(Pos(x, y)) == Bug {
                     if Pos(x, y)
                         .neighbors()
-                        .into_iter()
+                        .iter()
                         .filter(|p| self.at(**p) == Bug)
                         .count()
                         != 1
@@ -238,7 +238,7 @@ impl Life {
                 } else {
                     let count = Pos(x, y)
                         .neighbors()
-                        .into_iter()
+                        .iter()
                         .filter(|p| self.at(**p) == Bug)
                         .count();
                     if count == 1 || count == 2 {