Use async instead of defer for analytics script

We had this issue on Impress 2020 and I fixed it over there too. I guess
it went less noticed here on Classic, because it's a more
progressively-enhanced site in general (and this failure case is an
interesting argument for that architecture! lol).

On Impress 2020, I wasn't sure if the "waits for the document to load"
behavior of the `defer` attribute was necessary to the script, so I
chose to keep `defer` but move it _after_ the other scripts.

This time, I dug in a bit more, and found a Plausible author saying
that the choice was kinda arbitrary; and another person who had the
same issue as me, who said they switched to `async` and it worked well.
So, that's what we're doing now, too!

https://github.com/plausible/analytics/discussions/1907#discussioncomment-2754499

app/assets/javascripts/pets/bulk.js

@@ -1,5 +1,14 @@
 var DEBUG = document.location.search.substr(0, 6) == "?debug";
 
+function petThumbnailUrl(pet_name) {
+  // if first character is "@", use the hash url
+  if (pet_name[0] == "@") {
+    return "https://pets.neopets.com/cp/" + pet_name.substr(1) + "/1/1.png";
+  }
+
+  return "https://pets.neopets.com/cpn/" + pet_name + "/1/1.png";
+}
+
 /* Needed items form */
 (function () {
   var UI = {};
@@ -65,10 +74,6 @@ var DEBUG = document.location.search.substr(0, 6) == "?debug";
     loadItems(data.query);
   }
 
-  function petThumbnailUrl(pet_name) {
-    return "https://pets.neopets.com/cpn/" + pet_name + "/1/1.png";
-  }
-
   /* Items */
 
   function loadItems(query) {
@@ -127,7 +132,7 @@ var DEBUG = document.location.search.substr(0, 6) == "?debug";
 
     function Pet(name) {
       var el = $("#bulk-pets-submission-template")
-        .tmpl({ pet_name: name })
+        .tmpl({ pet_name: name, pet_thumbnail: petThumbnailUrl(name) })
         .appendTo(queue_el);
 
       this.load = function () {

app/views/application/_analytics.html.erb

@@ -1,2 +1,2 @@
 <%= javascript_include_tag 'https://analytics.openneo.net/js/script.js',
-    defer: true, 'data-domain': 'impress.openneo.net' %>
+    async: true, 'data-domain': 'impress.openneo.net' %>

app/views/pets/bulk.html.haml

@@ -68,7 +68,7 @@
   
   %script#bulk-pets-submission-template{:type => 'text/x-jquery/tmpl'}
     %li.waiting
-      %img{:src => 'https://pets.neopets.com/cpn/${pet_name}/1/1.png'}
+      %img{:src => '${pet_thumbnail}'}
       %span.name ${pet_name}
       %span.waiting-message= t '.bulk_pets.waiting'
       %span.loading-message= t '.bulk_pets.loading'