Function dbstat_bytes_for_scan_group 

fn dbstat_bytes_for_scan_group(
    conn: &Connection,
    scan_table: &str,
    item_table: &str,
) -> Option<u64>

Approximate on-disk bytes for btree objects (table + indexes) for scan_table + item_table. Uses SQLite dbstat when available. Returns None if dbstat is not compiled in (caller splits DB file size by row count).