Function extract_max_seq 

pub fn extract_max_seq(
    rows: &[HashMap<String, KalamCellValue>],
) -> Option<SeqId>

Extract the maximum _seq value from a slice of named-column rows.

Returns None when no row contains a parseable _seq value.

let max = extract_max_seq(&rows);
if let Some(seq) = max {
    entry.last_seq_id = Some(seq);
}