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/setup.go

@@ -29,10 +29,10 @@ func setup(c *caddy.Controller) error {
 		if t == nil {
 			return nil
 		}
-		f.transfer = t.(*transfer.Transfer) // if found this must be OK.
+		f.Xfer = t.(*transfer.Transfer) // if found this must be OK.
 		go func() {
 			for _, n := range zones.Names {
-				f.transfer.Notify(n)
+				f.Xfer.Notify(n)
 			}
 		}()
 		return nil
@@ -45,7 +45,7 @@ func setup(c *caddy.Controller) error {
 		}
 		go func() {
 			for _, n := range zones.Names {
-				f.transfer.Notify(n)
+				f.Xfer.Notify(n)
 			}
 		}()
 		return nil
@@ -55,7 +55,7 @@ func setup(c *caddy.Controller) error {
 		z := zones.Z[n]
 		c.OnShutdown(z.OnShutdown)
 		c.OnStartup(func() error {
-			z.StartupOnce.Do(func() { z.Reload(f.transfer) })
+			z.StartupOnce.Do(func() { z.Reload(f.Xfer) })
 			return nil
 		})
 	}