Use batch add for Tumble task queue tasks.

tumble/fire_tasks.go

Index: tumble/fire_tasks.go
diff --git a/tumble/fire_tasks.go b/tumble/fire_tasks.go
index e0ba079b880cfc0da0df516e8e79a51a0f9f5384..15ee6e3324c2f14d1ad92648d9dbb933935d4266 100644
--- a/tumble/fire_tasks.go
+++ b/tumble/fire_tasks.go
@@ -78,7 +78,8 @@ func fireTasks(c context.Context, cfg *Config, shards map[taskShard]struct{}) bo
 		logging.Infof(c, "added task %q %s %s", tsk.Name, tsk.Path, tsk.ETA)
 	}
 
-	if err := errors.Filter(tq.Add(ds.WithoutTransaction(c), baseName, tasks...), tq.ErrTaskAlreadyAdded); err != nil {
+	b := tq.Batcher{}
+	if err := errors.Filter(b.Add(ds.WithoutTransaction(c), baseName, tasks...), tq.ErrTaskAlreadyAdded); err != nil {
 		logging.Warningf(c, "attempted to fire tasks %v, but failed: %s", shards, err)
 		return false
 	}