Track completed statuses (#111)

For some devices there may be an additional status update broadcast
after the on_complete callback. This causes the status to be added
back to the dictionary where it will never be removed.

Track which statuses have been completed and check this set when
updating to ensure that a completed status is never added back to
the snapshot after on_complete is called.

src/blueapi/worker/reworker.py

@@ -4,7 +4,7 @@
 from functools import partial
 from queue import Full, Queue
 from threading import Event, RLock
-from typing import Any, Dict, Iterable, List, Mapping, Optional, Union
+from typing import Any, Dict, Iterable, List, Mapping, Optional, Set, Union
 
 from bluesky.protocols import Status
 
@@ -54,6 +54,7 @@ class RunEngineWorker(Worker[Task]):
     _current: Optional[ActiveTask]
     _status_lock: RLock
     _status_snapshot: Dict[str, StatusView]
+    _completed_statuses: Set[str]
     _worker_events: EventPublisher[WorkerEvent]
     _progress_events: EventPublisher[ProgressEvent]
     _data_events: EventPublisher[DataEvent]
@@ -79,6 +80,7 @@ def __init__(
         self._data_events = EventPublisher()
         self._status_lock = RLock()
         self._status_snapshot = {}
+        self._completed_statuses = set()
         self._started = Event()
         self._stopping = Event()
         self._stopped = Event()
@@ -152,6 +154,7 @@ def _cycle(self) -> None:
         self._report_status()
         self._errors.clear()
         self._warnings.clear()
+        self._completed_statuses.clear()
 
     @property
     def worker_events(self) -> EventStream[WorkerEvent, int]:
@@ -240,6 +243,7 @@ def _monitor_status(self, status: Status) -> None:
             def on_complete(status: Status) -> None:
                 self._on_status_event(status, status_uuid)
                 del self._status_snapshot[status_uuid]
+                self._completed_statuses.add(status_uuid)
 
             status.add_callback(on_complete)  # type: ignore
 
@@ -274,8 +278,10 @@ def _on_status_event(
             time_elapsed=time_elapsed,
             time_remaining=time_remaining,
         )
-        self._status_snapshot[status_uuid] = view
-        self._publish_status_snapshot()
+        # Ensure completed statues are not re-added and published
+        if status_uuid not in self._completed_statuses:
+            self._status_snapshot[status_uuid] = view
+            self._publish_status_snapshot()
 
     def _publish_status_snapshot(self) -> None:
         if self._current is None: