Task handler will automatically remove uncalled but canceled from task handler. By default this will not occur until a canceled task has been uncalled for 60 second after the time it should have been called. To adjust this time use TASK_HANDLER.stale_timeout. If stale_timeout is 0 stale tasks will not be automatically removed.
This is not done on a timer. I is done as new tasks are added or the load method is called.
Added unit tests to test automatic removal. Including when it should not automatically removed. Both when it is too soon, or when the stale_timeout attribute is set to 0.
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