如何在firestore objective-c上设置/更新数据时获取以秒为单位的Firebase服务器时间？

@import Firebase;
@import FirebaseFirestore;

FIRFirestore *firestore = [FIRFirestore firestore];
FIRTimestamp *serverTimestamp = [FIRTimestamp timestamp];

FIRDocumentReference *docRef = [firestore collectionWithPath:@"your_collection"].documentWithPath:@"your_document"];
[docRef setData:@{@"timestamp": serverTimestamp} merge:YES completion:^(NSError * _Nullable error) {
    if (error != nil) {
        NSLog(@"Error updating document: %@", error);
    } else {
        NSLog(@"Document updated successfully.");
    }
}];