DEV: Prefabrication (test optimization) (#7414)

* Introduced fab!, a helper that creates database state for a group

It's almost identical to let_it_be, except:

 1. It creates a new object for each test by default,
 2. You can disable it using PREFABRICATION=0

spec/requests/permalinks_controller_spec.rb

@@ -3,8 +3,8 @@
 require 'rails_helper'
 
 describe PermalinksController do
-  let(:topic) { Fabricate(:topic) }
-  let(:permalink) { Fabricate(:permalink, url: "deadroutee/topic/546") }
+  fab!(:topic) { Fabricate(:topic) }
+  fab!(:permalink) { Fabricate(:permalink, url: "deadroutee/topic/546") }
 
   describe 'show' do
     it "should redirect to a permalink's target_url with status 301" do