Move #preserve_finished_jobs? to SolidQueue module for consistency

With the other boolean options.

Author: rosa

app/models/solid_queue/job/executable.rb

@@ -78,7 +78,7 @@ def dispatch_bypassing_concurrency_limits
       end
 
       def finished!
-        if preserve_finished_jobs?
+        if SolidQueue.preserve_finished_jobs?
           touch(:finished_at)
         else
           destroy!
@@ -117,10 +117,6 @@ def ready
         def execution
           %w[ ready claimed failed ].reduce(nil) { |acc, status| acc || public_send("#{status}_execution") }
         end
-
-        def preserve_finished_jobs?
-          SolidQueue.preserve_finished_jobs
-        end
     end
   end
 end

lib/solid_queue.rb

@@ -34,11 +34,17 @@ module SolidQueue
   mattr_accessor :clear_finished_jobs_after, default: 1.day
   mattr_accessor :default_concurrency_control_period, default: 3.minutes
 
-  def self.supervisor?
-    supervisor
-  end
-
-  def self.silence_polling?
-    silence_polling
+  class << self
+    def supervisor?
+      supervisor
+    end
+
+    def silence_polling?
+      silence_polling
+    end
+
+    def preserve_finished_jobs?
+      preserve_finished_jobs
+    end
   end
 end