impl FusedIterator for Permutations

The lazy buffer fuses the iterator so `I` does not have to be fused.

src/permutations.rs

@@ -1,6 +1,7 @@
 use alloc::vec::Vec;
 use std::fmt;
 use std::iter::once;
+use std::iter::FusedIterator;
 
 use super::lazy_buffer::LazyBuffer;
 use crate::size_hint::{self, SizeHint};
@@ -131,6 +132,13 @@ where
     }
 }
 
+impl<I> FusedIterator for Permutations<I>
+where
+    I: Iterator,
+    I::Item: Clone,
+{
+}
+
 fn advance(indices: &mut [usize], cycles: &mut [usize]) -> bool {
     let n = indices.len();
     let k = cycles.len();