Add "Lines Changed" column to "Pull requests to review" list

Problem: As a code reviewer, I'm often faced with performing PR triage, working my way through a significant number of PRs that require my approval. It would be handy if I could identify tiny PRs (eg, a 1-line dependency bump) to approve quickly so they're not bottle-necked by the larger PRs.

Proposed Solution: Add a "Lines changed" column to the "Pull requests to review" list, displaying total number of lines added and total number of lines removed (similar to the indicator shown next to each file changed inside a PR).