Function parse_duration_to_seconds 

pub fn parse_duration_to_seconds(s: &str) -> Option<u64>

Parses a duration string to seconds.

Supported formats:

• “0” or “” - No expiration (returns Some(0))
• “30d” - 30 days
• “7d” - 7 days
• “24h” - 24 hours
• “60m” - 60 minutes
• “3600s” or “3600” - 3600 seconds

Returns

• Some(0) for “0” or empty string (explicitly no expiration)
• Some(seconds) for valid duration strings
• None for invalid formats (caller should use default)