test-store [nfc]: Add removeUser and updateUser extension methods on PerAccountStore

Author: sm-sayedi

test/model/test_store.dart

@@ -129,6 +129,14 @@ extension PerAccountStoreTestExtension on PerAccountStore {
     }
   }
 
+  Future<void> removeUser(int userId) async {
+    await handleEvent(RealmUserRemoveEvent(id: 1, userId: userId));
+  }
+
+  Future<void> updateUser(int userId, {String? fullName}) async {
+    await handleEvent(RealmUserUpdateEvent(id: 1, userId: userId, fullName: fullName));
+  }
+
   Future<void> addStream(ZulipStream stream) async {
     await addStreams([stream]);
   }