Improve performance on summing adjustments and payment

:amount is a database field in these cases, as opposed to a method that returns a computed result. Calling `.sum(:amount)` is much more efficient here as it computes the sum at database level, as opposed to `.map(&:amount).sum`, which would fetch and instanciate all the objects first, and then sum the amounts after.

app/helpers/checkout_helper.rb

@@ -19,7 +19,7 @@ module CheckoutHelper
     adjustments.reject! { |a| a.originator_type == 'EnterpriseFee' && a.source_type != 'Spree::LineItem' }
     unless exclude.include? :admin_and_handling
       adjustments << Spree::Adjustment.new(
-        label: I18n.t(:orders_form_admin), amount: enterprise_fee_adjustments.map(&:amount).sum
+        label: I18n.t(:orders_form_admin), amount: enterprise_fee_adjustments.sum(:amount)
       )
     end
 
@@ -28,7 +28,7 @@ module CheckoutHelper
 
   def display_checkout_admin_and_handling_adjustments_total_for(order)
     adjustments = order.adjustments.eligible.where('originator_type = ? AND source_type != ? ', 'EnterpriseFee', 'Spree::LineItem')
-    Spree::Money.new adjustments.map(&:amount).sum, currency: order.currency
+    Spree::Money.new adjustments.sum(:amount), currency: order.currency
   end
 
   def checkout_line_item_adjustments(order)
@@ -36,7 +36,7 @@ module CheckoutHelper
   end
 
   def checkout_subtotal(order)
-    order.item_total + checkout_line_item_adjustments(order).map(&:amount).sum
+    order.item_total + checkout_line_item_adjustments(order).sum(:amount)
   end
 
   def display_checkout_subtotal(order)

app/models/spree/order.rb

@@ -397,11 +397,11 @@ module Spree
     end
 
     def ship_total
-      adjustments.shipping.map(&:amount).sum
+      adjustments.shipping.sum(:amount)
     end
 
     def tax_total
-      adjustments.tax.map(&:amount).sum
+      adjustments.tax.sum(:amount)
     end
 
     # Creates new tax charges if there are any applicable rates. If prices already

engines/order_management/app/services/order_management/order/updater.rb

@@ -55,9 +55,9 @@ module OrderManagement
       # - adjustment_total - total value of all adjustments
       # - total - order total, it's the equivalent to item_total plus adjustment_total
       def update_totals
-        order.payment_total = payments.completed.map(&:amount).sum
+        order.payment_total = payments.completed.sum(:amount)
         order.item_total = line_items.map(&:amount).sum
-        order.adjustment_total = adjustments.eligible.map(&:amount).sum
+        order.adjustment_total = adjustments.eligible.sum(:amount)
         order.total = order.item_total + order.adjustment_total
       end