Okay, I've simplified the migration to *just* add the column, and
instead added a task to find assets without manifest URLs and backfill
them.
Performance is a lot better now, using the `async-http` library, which
as I understand it supports both persistent connections when invoked
like this, and maybe also HTTP/2 multiplexing?? (Though I'm not
actually sure images.neopets.com does lol)
I'm not sure about the number of concurrent tasks I picked here, 100
seems okay for an internet thing and for such small requests, but I
worry that the CDN is gonna get annoyed or something. Well, we'll see!
This task is very resumable if it turns out we get frozen out or
something.
Matchu
dc22a458bf