DEV: Make every DistributedCache lazily instantiated (#23147)

app/models/category.rb

@@ -205,14 +205,16 @@ class Category < ActiveRecord::Base
   # Allows us to skip creating the category definition topic in tests.
   attr_accessor :skip_category_definition
 
-  @topic_id_cache = DistributedCache.new("category_topic_ids")
+  def self.topic_id_cache
+    @topic_id_cache ||= DistributedCache.new("category_topic_ids")
+  end
 
   def self.topic_ids
-    @topic_id_cache.defer_get_set("ids") { Set.new(Category.pluck(:topic_id).compact) }
+    topic_id_cache.defer_get_set("ids") { Set.new(Category.pluck(:topic_id).compact) }
   end
 
   def self.reset_topic_ids_cache
-    @topic_id_cache.clear
+    topic_id_cache.clear
   end
 
   def reset_topic_ids_cache

app/models/developer.rb

@@ -6,14 +6,16 @@ class Developer < ActiveRecord::Base
   after_save :rebuild_cache
   after_destroy :rebuild_cache
 
-  @id_cache = DistributedCache.new("developer_ids")
+  def self.id_cache
+    @id_cache ||= DistributedCache.new("developer_ids")
+  end
 
   def self.user_ids
-    @id_cache.defer_get_set("ids") { Set.new(Developer.pluck(:user_id)) }
+    id_cache.defer_get_set("ids") { Set.new(Developer.pluck(:user_id)) }
   end
 
   def self.rebuild_cache
-    @id_cache.clear
+    id_cache.clear
   end
 
   def rebuild_cache

app/models/theme.rb

@@ -10,7 +10,9 @@ class Theme < ActiveRecord::Base
 
   attr_accessor :child_components
 
-  @cache = DistributedCache.new("theme:compiler:#{BASE_COMPILER_VERSION}")
+  def self.cache
+    @cache ||= DistributedCache.new("theme:compiler:#{BASE_COMPILER_VERSION}")
+  end
 
   belongs_to :user
   belongs_to :color_scheme
@@ -202,7 +204,7 @@ class Theme < ActiveRecord::Base
   end
 
   def self.get_set_cache(key, &blk)
-    @cache.defer_get_set(key, &blk)
+    cache.defer_get_set(key, &blk)
   end
 
   def self.theme_ids
@@ -369,7 +371,7 @@ class Theme < ActiveRecord::Base
   end
 
   def self.clear_cache!
-    @cache.clear
+    cache.clear
   end
 
   def self.targets