Move backorder amendment out of order callback

Triggering it for each order is inefficient when we cancel them in bulk.
The callback doesn't allow us to optimise this.

app/controllers/spree/admin/orders_controller.rb

@@ -70,6 +70,7 @@ module Spree
         @order.restock_items = params.fetch(:restock_items, "true") == "true"
 
         if @order.public_send(event.to_s)
+          AmendBackorderJob.perform_later(@order) if event == "cancel"
           flash[:success] = Spree.t(:order_updated)
         else
           flash[:error] = Spree.t(:cannot_perform_operation)

app/models/spree/order/checkout.rb

@@ -142,8 +142,6 @@ module Spree
 
             OrderMailer.cancel_email(id).deliver_later if send_cancellation_email
             update(payment_state: updater.update_payment_state)
-
-            AmendBackorderJob.perform_later(self)
           end
 
           def after_resume

app/services/orders/bulk_cancel_service.rb

@@ -15,6 +15,7 @@ module Orders
         order.send_cancellation_email = @send_cancellation_email
         order.restock_items = @restock_items
         order.cancel
+        AmendBackorderJob.perform_later(order)
       end
       # rubocop:enable Rails/FindEach
     end

app/services/orders/customer_cancellation_service.rb

@@ -10,6 +10,7 @@ module Orders
       return unless order.cancel
 
       Spree::OrderMailer.cancel_email_for_shop(order).deliver_later
+      AmendBackorderJob.perform_later(order)
     end
 
     private