Function parse_line 

pub(crate) fn parse_line<T: DbAddress>(
    line: &str,
) -> Result<Option<(RangeInclusive<T::Int>, Option<CountryCode>, Option<NonZeroU32>)>, Error>
where
    Error: From<<T as FromStr>::Err>,

Parse a single line from a database, expecting addresses of type T.

Return Ok(None) if the line is empty.