* Requeue UMP queue items if weight exhausted

* Reduce complexity and remove Deque

* Formatting

* Formatting

* Avoid needless storage writes

* Test

* Formatting

* Docs and cleanup

* fmt

* Remove now irrelevant comment.

* Simplify `take_processed` by using `mem::take`

* Clean up & fmt: use `upward_message` directly.

* Grumbles

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Sergei Shulepov <sergei@parity.io>