Move lifetime of take_iter from iterator to its items

[dariocurr]

Which issue does this PR close?

No issue, just small improvements.

Rationale for this change

Running cargo miri I saw some warnings regarding those lifetimes

42 |     pub fn take_iter<'a>(
   |                      -- lifetime `'a` declared here
...
45 |     ) -> impl Iterator<Item = Option<&str>> + 'a {
   |                                      ^ this elided lifetime gets resolved as `'a`

More in detail:

• impl Iterator<Item = Option<&[T>> + 'a ties the lifetime 'a to the iterator itself, but not necessarily to the items it yields
• impl Iterator<Item = Option<&'a T>> ties the lifetime 'a to the items yielded by the iterator

The latter is preferred

What changes are included in this PR?

Lifetimes moved from the iterator to the items it yields

Are there any user-facing changes?

No

[alamb]

Thank you @dariocurr - this makes sense to me