Move cache_key to the new cacheable concern

app/models/card.rb

@@ -41,10 +41,6 @@ class Card < ApplicationRecord
 
   delegate :accessible_to?, to: :collection
 
-  def cache_key
-    [ super, collection.name ].compact.join("/")
-  end
-
   def card
     self
   end

app/models/card/cacheable.rb

@@ -1,6 +1,10 @@
 module Card::Cacheable
   extend ActiveSupport::Concern
 
+  def cache_key
+    [ super, collection.name ].compact.join("/")
+  end
+
   def cache_invalidation_parts
     @cache_invalidation_parts ||= InvalidationParts.new(self)
   end