message: fix(client): avoid panics in uses of `Instant`
  Even though this is almost definitely a bug in Rust, it seems most
  prudent to actively avoid the uses of `Instant` that are prone to this
  bug.
  This change replaces uses of `Instant::elapsed` and `Instant::sub` with
  calls to `Instant::saturating_duration_since` to prevent this class of
  panic.
diff: @@ -458,7 +458,9 @@ impl<T: Poolable> PoolInner<T> {
  trace!("idle interval evicting closed for {:?}", key);
  return false;
  }
  - if now - entry.idle_at > dur {
  +
  + // Avoid `Instant::sub` to avoid issues like rust-lang/rust#86470.
  + if now.saturating_duration_since(entry.idle_at) > dur {
  trace!("idle interval evicting expired for {:?}", key);
  return false;
  }
  @@ -721,7 +723,8 @@ impl Expiration {
  fn expires(&self, instant: Instant) -> bool {
  match self.0 {
  - Some(timeout) => instant.elapsed() > timeout,
  + // Avoid `Instant::elapsed` to avoid issues like rust-lang/rust#86470.
  + Some(timeout) => Instant::now().saturating_duration_since(instant) > timeout,
  None => false,
  }
  }
  