Function create_new_file_stream 

fn create_new_file_stream(
    base_output_path: &ListingTableUrl,
    write_id: &str,
    part_idx: usize,
    file_extension: &str,
    single_file_output: bool,
    max_buffered_batches: usize,
    tx: &mut UnboundedSender<(Path, Receiver<RecordBatch>)>,
) -> Result<Sender<RecordBatch>>

Helper for row count demuxer