[Thread] make the Manager and Controller class 'final'

Per the API review council, the classes should be "final" by default

Bug: 301076593
Test: build && atest CtsThreadNetworkTestCases
Change-Id: I85f0b4fabe5b1bcec2be052620b38a07c58181d7
diff --git a/framework-t/api/system-current.txt b/framework-t/api/system-current.txt
index 6c98a4f..23510e1 100644
--- a/framework-t/api/system-current.txt
+++ b/framework-t/api/system-current.txt
@@ -492,12 +492,12 @@
     field @NonNull public static final android.os.Parcelable.Creator<android.net.thread.PendingOperationalDataset> CREATOR;
   }
 
-  @FlaggedApi("com.android.net.thread.flags.thread_enabled") public class ThreadNetworkController {
+  @FlaggedApi("com.android.net.thread.flags.thread_enabled") public final class ThreadNetworkController {
     method public int getThreadVersion();
     field public static final int THREAD_VERSION_1_3 = 4; // 0x4
   }
 
-  @FlaggedApi("com.android.net.thread.flags.thread_enabled") public class ThreadNetworkManager {
+  @FlaggedApi("com.android.net.thread.flags.thread_enabled") public final class ThreadNetworkManager {
     method @NonNull public java.util.List<android.net.thread.ThreadNetworkController> getAllThreadNetworkControllers();
   }