[PERF] Speed up integer type 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.

type_cast_from_database (small)  3437507.5 (±29.2%) i/s -   14223135 in   4.996973s
type_cast_from_database (large)  3158588.7 (±28.3%) i/s -   13265628 in   4.992121s
type_cast (small)                 481984.8 (±14.2%) i/s -    2352012 in   5.005694s
type_cast (large)                 477331.8 (±14.2%) i/s -    2332824 in   5.012365s

Comparison:
type_cast_from_database (small):  3437507.5 i/s
type_cast_from_database (large):  3158588.7 i/s - 1.09x slower
type_cast (small):                 481984.8 i/s - 7.13x slower
type_cast (large):                 477331.8 i/s - 7.20x slower

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

@@ -12,7 +12,9 @@ def type
         :integer
       end
 
-      alias type_cast_for_database type_cast
+      def type_cast_from_database(value)
+        value.to_i unless value.nil?
+      end
 
       protected