Function to_parquet 

pub fn to_parquet(
    dumps: &[Loaded],
    output: &Path,
    host: &str,
    zstd_level: i32,
) -> Result<usize>

Writes the records of one or more loaded dumps to output as one sparse-wide Parquet table. Returns the total row count. host overrides the dumps’ host label in the footer when non-empty. zstd_level is the zstd compression level (1–22).