Refactor RuboCop configuration, update Puma plugin to use $PROCESS_ID, and simplify ORM setter in RabbitCarrots configuration

.rubocop.yml

@@ -111,3 +111,7 @@ Metrics/CyclomaticComplexity:
   Max: 15
 Metrics/PerceivedComplexity:
   Max: 15
+Metrics/ClassLength:
+  Max: 150
+Metrics/ParameterLists:
+  Max: 6

lib/puma/plugin/rabbit_carrots.rb

@@ -1,4 +1,5 @@
 # rabbit_carrots.rb
+require 'English'
 require 'puma/plugin'
 require 'rabbit_carrots'
 
@@ -7,7 +8,7 @@ Puma::Plugin.create do
 
   def start(launcher)
     @log_writer = launcher.log_writer
-    @puma_pid = $$
+    @puma_pid = $PROCESS_ID
 
     @core_service = RabbitCarrots::Core.new(logger: log_writer)
 
@@ -57,7 +58,7 @@ Puma::Plugin.create do
     loop do
       if send(process_dead)
         log message
-        Process.kill('TERM', $$)
+        Process.kill('TERM', $PROCESS_ID)
         break
       end
       sleep 2

lib/rabbit_carrots/configuration.rb

@@ -24,8 +24,6 @@ module RabbitCarrots
       @orm ||= :activerecord
     end
 
-    def orm=(value)
-      @orm = value
-    end
+    attr_writer :orm
   end
 end

lib/rabbit_carrots/connection.rb

@@ -3,6 +3,7 @@ require 'singleton'
 module RabbitCarrots
   class Connection
     include ::Singleton
+
     attr_reader :connection
 
     def initialize