message: Fix a few clippy warnings
  The warnings were `into_iter_on_ref` and `identity_conversion`
diff: @@ -279,7 +279,7 @@ impl<'a, N: 'a> IntoSparseVecIter<'a, N> for &'a [N] {
  }
  fn into_sparse_vec_iter(self) -> Enumerate<Iter<'a, N>> {
  - self.into_iter().enumerate()
  + self.iter().enumerate()
  }
  fn is_dense(&self) -> bool {
  @@ -299,7 +299,7 @@ impl<'a, N: 'a> IntoSparseVecIter<'a, N> for &'a Vec<N> {
  }
  fn into_sparse_vec_iter(self) -> Enumerate<Iter<'a, N>> {
  - self.into_iter().enumerate()
  + self.iter().enumerate()
  }
  fn is_dense(&self) -> bool {
  @@ -768,7 +768,7 @@ where
  .sum()
  } else {
  let mut lhs_iter = self.iter();
  - let mut rhs_iter = rhs.into_sparse_vec_iter().into_iter();
  + let mut rhs_iter = rhs.into_sparse_vec_iter();
  let mut sum = N::zero();
  let mut left_nnz = lhs_iter.next();
  let mut right_nnz = rhs_iter.next();
  