Function to_csv 

pub fn to_csv(records: &[Record], booleans: BoolStyle) -> String

Export records as the compact mapping CSV.

The header is prn,norad_cat_id,active,sp3_id. The active column is true only when both active and usable hold. Records are sorted by (system, prn); the system is encoded in the sp3_id letter, so equal PRNs across systems are ordered deterministically without a separate column.