Convert between different timestamp formats
Unix Timestamp (Seconds): Seconds elapsed since January 1, 1970, 00:00:00 UTC.
Unix Timestamp (Milliseconds): Milliseconds elapsed since January 1, 1970, 00:00:00 UTC.
ISO 8601: International standard date format (YYYY-MM-DDTHH:mm:ss.sssZ).
Relative Time: Time relative to the current moment (e.g., "2 hours ago").