@pierre/diffs 1.3 + async diff highlighting

[david-crespo]

• Fetch full file contents only when a hunk is expanded, instead of fetching and tokenizing files as they enter the render window
• Run highlighting in a worker pool so large diffs don’t block the UI

Seems to be faster. One notable improvement: pressing n to move on from a very large file diff (like a lockfile) had a noticeable delay before, now it doesn't.