Cache the result of is_sharded?

It can't possibly change.... and it's eating ~2% of Classic's CPU?????

lib/active_record_shards/model.rb

@@ -10,8 +10,12 @@ def not_sharded
       self.sharded = false
     end
 
+    class_attribute :_model_class_is_sharded, default: nil
     def is_sharded? # rubocop:disable Naming/PredicateName
-      if self == ActiveRecord::Base
+      cached = self.class._model_class_is_sharded
+      return cached unless cached.nil?
+
+      cached = if self == ActiveRecord::Base
         sharded != false && supports_sharding?
       elsif self == base_class
         if sharded.nil?
@@ -22,6 +26,9 @@ def is_sharded? # rubocop:disable Naming/PredicateName
       else
         base_class.is_sharded?
       end
+
+      self.class._model_class_is_sharded = cached
+      cached
     end
 
     def on_replica_by_default?