message: Make SmallSet return ExactSizeIterator
  Summary: ^
diff: @@ -95,11 +95,11 @@ impl<T> SmallSet<T> {
  Self(SmallMap::with_capacity(n))
  }
  - pub fn iter(&self) -> impl Iterator<Item = &T> + Clone {
  + pub fn iter(&self) -> impl ExactSizeIterator<Item = &T> + Clone {
  self.0.keys()
  }
  - pub fn into_iter(self) -> impl Iterator<Item = T> {
  + pub fn into_iter(self) -> impl ExactSizeIterator<Item = T> {
  self.0.into_iter().map(|(t, _)| t)
  }
  