As a developer
I want to know which pulls I should look at
So that I can avoid wasting effort by forgetting to come back to partially-reviewed pulls
Let's add a tag which immediately marks a pull as having an out-of-date CR from that dev. This makes it easy to both reserve pulls (if you're in the middle of a CR on them) and to mark pulls which you've been involved in (to avoid duplication of effort from other devs).