add proper divisors into_iter

lib/proper_divisors/src/lib.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, hash_map};
 
 #[derive(Debug)]
 pub struct ProperDivisors {
@@ -43,6 +43,10 @@ impl ProperDivisors {
     pub fn get(&self, number: usize) -> &[usize] {
         self.map.get(&number).unwrap()
     }
+
+    pub fn into_iter(self) -> hash_map::IntoIter<usize, Vec<usize>> {
+        self.map.into_iter()
+    }
 }
 
 #[cfg(test)]