Function format_iso 

pub fn format_iso(ts: DateTime<Utc>) -> String

Formats a DateTime<Utc> using the global timezone.

Format: %Y-%m-%dT%H:%M:%S%:z (e.g. 2026-04-19T10:00:00+00:00 for UTC, 2026-04-19T07:00:00-03:00 for America/Sao_Paulo).