Add Unique Queue infrastructure and move TestPullRequests to this (#9856)
* Upgrade levelqueue to version 0.2.0
This adds functionality for Unique Queues
* Add UniqueQueue interface and functions to create them
* Add UniqueQueue implementations
* Move TestPullRequests over to use UniqueQueue
* Reduce code duplication
* Add bytefifos
* Ensure invalid types are logged
* Fix close race in PersistableChannelQueue Shutdown
guillep2k
John Olheiser
6543
zeripath
Lunny Xiao
Tamal Saha