Speed up integer casting from DB

We don't have the check the range when the value is coming from the DB,
so override type_cast_from_database to short-circuit the extra work.
The difference is huge but the absolute gain is quite small. That being
said this is a hotspot and it showed up on the radar when benchmarking
discourse.

activerecord/lib/active_record/type/integer.rb

@@ -14,6 +14,11 @@ module ActiveRecord
 
       alias type_cast_for_database type_cast
 
+      def type_cast_from_database(value)
+        return if value.nil?
+        value.to_i
+      end
+
       protected
 
       attr_reader :range