Function expiry_timestring_to_unix_nanos 

pub fn expiry_timestring_to_unix_nanos(
    expiry: &str,
    details: Option<&ContractDetails>,
) -> Result<UnixNanos>

Convert timestamp string to UnixNanos.

Handles formats like “20230101” or “20230101 00:00:00 UTC”.

Errors

Returns an error if the timestamp cannot be parsed.