Function run 

pub fn run(
    lf: LazyFrame,
    request: &ExportRequest,
    polars_streaming: bool,
    written: impl FnMut(u64) + Send + 'static,
) -> Result<()>

Run an export: plan lf for the format (ExportFormat::prepare), write by its Route, commit. written hears bytes so far (0 at start, then a few times a second). The destination changes only if everything was written.