I ran `rails zeitwerk:check`, which eager-loads the app, and it found two problems: `closet_group.rb` doesn't define `ClosetGroup` (cuz it's empty), and I left in a reference to a cache sweeper observer oops. Goodbye!
Some important little upgrades but mostly straightforward!
Note that there's still a known issue where item searches crash, I was hoping that this was a bug in Rails 4.2 that would be fixed on upgading to 5, but nope, oh well!
Also uhh I just got a bit silly and didn't actually mean to go all the way to 5.2 in one go, I had meant to start at 5.0… but tbh the 5.1 and 5.2 changes seem small, and this seems to be working, so. Yeah ok let's roll!
