Kudos do not update when kudos-giver changes username
Steps to reproduce
1. Log in
2. Browse > Works
3. Follow a title to access a work
4. At the bottom of the work, press "Kudos"
5. Hi, username! > My Preferences > Change My User Name
6. Fill in required information
7. Press "Change User Name"
8. Press "OK" to confirm the name change
9. Return to the work and notice your old username is still in the kudos list
What should happen
The username information in the kudos should switch to your new username as quickly as possible. (This might take a while, since we'll have to look up every work the user has kudosed. However, in terms of performance, we're okay with doing this.)
Kudos belong to users, so when the user_id remains the same but the login of the user changes, it's a plain old caching issue.
Kudos are cached in two places, and the cache key is dependent on whether the work has been updated:
The partial that is used at the bottom of the work: https://github.com/otwcode/otwarchive/blob/ff332552fadbec7161f5e0bd5a4c904f333ba88e/app/views/kudos/_kudos.html.erb#L4
The index that displays if you follow the "and # more users" link on works with lots of kudos, or which you can access by going to http://test.ao3.org/works/#####/kudos: https://github.com/otwcode/otwarchive/blob/ff332552fadbec7161f5e0bd5a4c904f333ba88e/app/views/kudos/index.html.erb#L7
If the work creator or an admin edits the work you've kudosed, that will expire the cached kudos section and your name will update to match your new username.
After AO3-5597, kudos are associated with users instead of pseuds. I'll remove the pseud-related scenarios in the issue description.