message: simplify the logic by using `changed_at` and not `verified_at`
  I think they are actually equivalent, as we have already fond that the
  inputs did not change in the range `changed_at..=verified_at`.
diff: @@ -128,11 +128,9 @@ where
  // first things first, let's walk over each of our previous
  // inputs and check whether they are out of date.
  if let Some(QueryState::Memoized(old_memo)) = &mut old_value {
  - if old_memo
  - .inputs
  - .iter()
  - .all(|old_input| !old_input.maybe_changed_since(query, old_memo.verified_at))
  - {
  + if old_memo.inputs.iter().all(|old_input| {
  + !old_input.maybe_changed_since(query, old_memo.stamped_value.changed_at)
  + }) {
  debug!("{:?}({:?}): inputs still valid", Q::default(), key);
  // If none of out inputs have changed since the last time we refreshed
  