some object allocation reduction for new AR objects

Benchmark:

```ruby
require 'objspace'
require 'active_record'

ActiveRecord::Base.establish_connection adapter: "sqlite3",
                                        database: ":memory:"

ActiveRecord::Base.connection.instance_eval do
  create_table(:articles) { |t| t.string :name }
end

class Article < ActiveRecord::Base; end
a = Article.create name: "foo"
a = Article.find a.id

N = 10
ObjectSpace::AllocationTracer.trace do
  N.times { Article.find a.id }
end
ObjectSpace::AllocationTracer.allocated_count_table
table.sort_by { |_,x| x }.each do |k,v|
  p k => (v / N)
end
```

1 files changed, 2 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index a9ddd9141f..45b6b1c925 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -37,7 +37,8 @@ module ActiveRecord
     #   Post.find_by_sql ["SELECT body FROM comments WHERE author = :user_id OR approved_by = :user_id", { :user_id => user_id }]
     def find_by_sql(sql, binds = [])
       result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds)
-      column_types = result_set.column_types.except(*columns_hash.keys)
+      column_types = result_set.column_types.dup
+      columns_hash.each_key { |k| column_types.delete k }
       result_set.map { |record| instantiate(record, column_types) }
     end