Function single_part_upload 

async fn single_part_upload<E: EventEmitter>(
    client: &Client,
    bucket: &BucketId,
    key: &str,
    source_path: &PathBuf,
    total_bytes: u64,
    request_id: &str,
    channel: &E,
    registry: &TransferRegistryHandle,
    cancel_flag: &AtomicBool,
) -> Result<(), AppError>