unset _pulsar on complete

to make sure we can copy.deepcopy the report
resolves https://git.geomar.de/digital-earth/dasf/dasf-messaging-python/-/merge_requests/37#note_40839

deprogressapi/base.py

@@ -255,6 +255,8 @@ class BaseReport(BaseModel):
         if self._window is not None:
             curses.endwin()
             self._window = None
+        if self._pulsar is not None:
+            self._pulsar = None
 
     def __enter__(self):
         self.status = Status.RUNNING