add dispose to files to remove controllers when not used

Frontend/patient_manager/lib/pages/register.dart

@@ -225,6 +225,15 @@ class _RegisterState extends State<Register> {
     });
   }
 
+  @override
+  void dispose() {
+    emailController.dispose();
+    passwordController.dispose();
+    officeID.dispose();
+    _focusNode.dispose();
+    super.dispose();
+  }
+
   @override
   Widget build(BuildContext context) {
     return KeyboardListener(