Clear resume token on some events known to be unprocessable.

This prevents hopeless retries. We should probably add other events to
this list, like OTHER, but we're currently not even using resume tokens,
so this is a TODO...

bosk-mongo/src/main/java/io/vena/bosk/drivers/mongo/v2/ChangeEventReceiver.java

@@ -272,6 +272,20 @@ private void eventProcessingLoop(Session session) {
 	}
 
 	private void processEvent(Session session, ChangeStreamDocument<Document> event) throws UnprocessableEventException {
+		switch (event.getOperationType()) {
+			case DROP:
+			case DROP_DATABASE:
+			case INVALIDATE:
+				// These events are hopeless. There is no way a resume could succeed.
+				// If we try, we'll simply cause another unnecessary reinitialization,
+				// which is not only wasteful, but can also cause the DisconnectedDriver
+				// retry to fail a second time and report a user-visible error. If we make
+				// sure not to try to re-process these events, we avoid all this.
+				lastProcessedResumeToken = event.getResumeToken();
+				break;
+			default:
+				break;
+		}
 		session.listener.onEvent(event);
 		lastProcessedResumeToken = event.getResumeToken();
 	}