Fix an N+1 in avatar URLs

This is tricky: the query was being run in
`ObjectStorage::Extension::RecordsUploads#retrieve_from_store!`, but we can't
just add batch loading there, because the `#upload=` method there would use the
result immediately, making the batch only have one item.

Instead, we can pre-emptively add an item to the batch whenever an avatarable
object is initialized, and then reuse that batch item in
`#retrieve_from_store!`. However, this also has problems:

1. There is a lot of logic in `Avatarable#retrieve_upload_from_batch`.
2. Some of that logic constructs a 'fake' model for the batch key. This should
   be fine, because of ActiveRecord's override of `#==`, but it relies on that
   staying the same.

1 files changed, 1 insertions, 0 deletions

diff --git a/app/models/personal_snippet.rb b/app/models/personal_snippet.rb
index 82c1c4de3a0..355624fd552 100644
--- a/app/models/personal_snippet.rb
+++ b/app/models/personal_snippet.rb
@@ -1,2 +1,3 @@
 class PersonalSnippet < Snippet
+  include WithUploads
 end