[macros] defcron use single thread for all runs

macros.lisp

@@ -148,6 +148,8 @@
                   (clon:make-typed-cron-schedule
                    ,@schedule)
                   :allow-now-p t)
-          :name ',name :thread t)
+          :name ',name
+          :thread (bt:make-thread (lambda () (loop (sleep 1)))
+                                  :name (format nil "Sleeper '~A'" (symbol-name ',name))))
          (values))
        (add-hook :starting ',scheduler))))