message: Use sort_unstable in sort_keys
  Summary: `sort_unstable` is cheaper than `sort`, and we don't need stable sort because keys are unique.
diff: @@ -244,7 +244,7 @@ impl<K, V> VecMap<K, V> {
  where
  K: Ord,
  {
  - self.buckets.sort_by(|a, b| a.key.cmp(&b.key));
  + self.buckets.sort_unstable_by(|a, b| a.key.cmp(&b.key));
  }
  pub(crate) fn is_sorted_by_key(&self) -> bool
  