feat(secondary): Send NOTIFY messages after zone transfer (#7901)

* feat(secondary): Send NOTIFY messages after zone transfer

- Modified TransferIn() method to accept a transfer.Transfer parameter
- Added NOTIFY message sending after successful zone transfer in secondary plugin
- Updated Update() method to pass the transfer handler through the zone update cycle
- Added comprehensive tests for the secondary notify functionality

Closes #5669

Signed-off-by: liucongran <liucongran327@gmail.com>

* fix(secondary): Fix TransferIn method call in test

Update test to pass nil parameter to TransferIn method after signature change

Signed-off-by: liucongran <liucongran327@gmail.com>

* refactor(secondary): Clean up imports and add helper methods

- Reorder imports for consistency
- Add hasSOA() and getSOA() helper methods to Zone
- Remove unnecessary blank lines in tests

Signed-off-by: liucongran <liucongran327@gmail.com>

* fix(test): Fix variable declaration in secondary test

Change corefile variable assignment to use short declaration syntax (:=)
to fix compilation error.

Signed-off-by: liucongran <liucongran327@gmail.com>

* refactor(secondary): Use getSOA helper method in shouldTransfer

Replace direct SOA access with getSOA() helper method for consistency.

Signed-off-by: liucongran <liucongran327@gmail.com>

---------

Signed-off-by: liucongran <liucongran327@gmail.com>
Co-authored-by: liucongran <liucongran@cestc.cn>

plugin/file/file.go

@@ -22,7 +22,7 @@ type (
 	File struct {
 		Next plugin.Handler
 		Zones
-		transfer *transfer.Transfer
+		Xfer *transfer.Transfer
 
 		Fall fall.F
 	}
@@ -70,7 +70,7 @@ func (f File) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (i
 			log.Infof("Notify from %s for %s: checking transfer", state.IP(), zone)
 			ok, err := z.shouldTransfer()
 			if ok {
-				z.TransferIn()
+				z.TransferIn(f.Xfer)
 			} else {
 				log.Infof("Notify from %s for %s: no SOA serial increase seen", state.IP(), zone)
 			}