Add Clone trait to Unique

Using a Unique iterator requires the Clone trait, so
require this trait when creating the Unique object.

src/unique_impl.rs

@@ -180,7 +180,7 @@ where
 pub fn unique<I>(iter: I) -> Unique<I>
 where
     I: Iterator,
-    I::Item: Eq + Hash,
+    I::Item: Eq + Hash + Clone,
 {
     Unique {
         iter: UniqueBy {

tests/test_std.rs

@@ -21,6 +21,22 @@ use rand::{
 use rand::{seq::SliceRandom, thread_rng};
 use std::{cmp::min, fmt::Debug, marker::PhantomData};
 
+#[test]
+fn unique_iterator() {
+    #[derive(Debug, PartialEq, Eq, Hash, Clone)]
+    struct Item {
+        value: u32,
+    }
+    impl Item {
+        fn new(value: u32) -> Item {
+            Item {value}
+        }
+    }
+    let data = std::vec![Item::new(1), Item::new(2), Item::new(3), Item::new(2)];
+    let data: Vec<_> = data.into_iter().unique().collect();
+    assert_eq!(data, std::vec![Item::new(1), Item::new(2), Item::new(3)]);
+}
+
 #[test]
 fn product3() {
     let prod = iproduct!(0..3, 0..2, 0..2);