enhance: Move forward l0 logic out of delta lock (#37337)

Related to #35303

`deleteMut` shall be protecting streaming delete buffer, forward l0
could be move out of the rlock section to reduce tsafe impact from
loading segments.

Signed-off-by: Congqi Xia <[email protected]>

internal/querynodev2/delegator/delegator_data.go

@@ -599,6 +599,15 @@ func (sd *shardDelegator) loadStreamDelete(ctx context.Context,
 	})
 	deltaPositions := req.GetDeltaPositions()
 
+	for _, info := range infos {
+		candidate := idCandidates[info.GetSegmentID()]
+		// forward l0 deletion
+		err := sd.forwardL0Deletion(ctx, info, req, candidate, targetNodeID, worker)
+		if err != nil {
+			return err
+		}
+	}
+
 	sd.deleteMut.RLock()
 	defer sd.deleteMut.RUnlock()
 	// apply buffered delete for new segments
@@ -628,12 +637,6 @@ func (sd *shardDelegator) loadStreamDelete(ctx context.Context,
 			deleteScope = querypb.DataScope_Streaming
 		}
 
-		// forward l0 deletion
-		err := sd.forwardL0Deletion(ctx, info, req, candidate, targetNodeID, worker)
-		if err != nil {
-			return err
-		}
-
 		deleteData := &storage.DeleteData{}
 		// start position is dml position for segment
 		// if this position is before deleteBuffer's safe ts, it means some delete shall be read from msgstream