Define Reloader class before callback that uses it (#4561)

If the application has already been loaded before this file is required,
the `after_initialize` callback runs immediately, but the Reloader class
isn't defined yet.

Also remove a comment about `cache_classes` that has been irrelevant
since 701e06224c.

lib/sidekiq/rails.rb

@@ -4,6 +4,22 @@ require "sidekiq/worker"
 
 module Sidekiq
   class Rails < ::Rails::Engine
+    class Reloader
+      def initialize(app = ::Rails.application)
+        @app = app
+      end
+
+      def call
+        @app.reloader.wrap do
+          yield
+        end
+      end
+
+      def inspect
+        "#<Sidekiq::Rails::Reloader @app=#{@app.class.name}>"
+      end
+    end
+
     # By including the Options module, we allow AJs to directly control sidekiq features
     # via the *sidekiq_options* class method and, for instance, not use AJ's retry system.
     # AJ retries don't show up in the Sidekiq UI Retries tab, save any error data, can't be
@@ -23,8 +39,6 @@ module Sidekiq
 
     # This hook happens after all initializers are run, just before returning
     # from config/environment.rb back to sidekiq/cli.rb.
-    # We have to add the reloader after initialize to see if cache_classes has
-    # been turned on.
     #
     # None of this matters on the client-side, only within the Sidekiq process itself.
     config.after_initialize do
@@ -32,21 +46,5 @@ module Sidekiq
         Sidekiq.options[:reloader] = Sidekiq::Rails::Reloader.new
       end
     end
-
-    class Reloader
-      def initialize(app = ::Rails.application)
-        @app = app
-      end
-
-      def call
-        @app.reloader.wrap do
-          yield
-        end
-      end
-
-      def inspect
-        "#<Sidekiq::Rails::Reloader @app=#{@app.class.name}>"
-      end
-    end
   end
 end