Add back thread observer

Author: npezza93

lib/solid_queue/pool.rb

@@ -19,16 +19,16 @@ def post(execution)
       available_threads.decrement
 
       future = Concurrent::Future.new(args: [ execution ], executor: executor) do |thread_execution|
-        begin
-          wrap_in_app_executor do
-            thread_execution.perform
-          end
-        rescue Exception
-          nil
-        ensure
-          available_threads.increment
-          mutex.synchronize { on_idle.try(:call) if idle? }
+        wrap_in_app_executor do
+          thread_execution.perform
         end
+      ensure
+        available_threads.increment
+        mutex.synchronize { on_idle.try(:call) if idle? }
+      end
+
+      future.add_observer do |_, _, error|
+        handle_thread_error(error) if error
       end
 
       future.execute