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/secondary_test.go

@@ -113,7 +113,7 @@ func TestTransferIn(t *testing.T) {
 	z.origin = testZone
 	z.TransferFrom = []string{s.Addr}
 
-	if err := z.TransferIn(); err != nil {
+	if err := z.TransferIn(nil); err != nil {
 		t.Fatalf("Unable to run TransferIn: %v", err)
 	}
 	if z.SOA.String() != fmt.Sprintf("%s	3600	IN	SOA	bla. bla. 250 0 0 0 0", testZone) {