make push_number_checked public to handle structured append

[RCasatta]

I need to generate qr codes for data up to 10kb or so, thus I need to split those with the structured append mode, I did a quick test but this need the method push_number_checked to be exposed

#[test]
    fn test_structured_append() {
        // from example https://segno.readthedocs.io/en/stable/structured-append.html#structured-append
        let data = "I read the news today oh boy".as_bytes();
        let data_half = "I read the new".as_bytes();
        let parity = data.iter().fold(0u8, |acc, &x| acc ^ x);
        let mut bits = Bits::new(Version::Normal(1));
        bits.push_mode_indicator(ExtendedMode::StructuredAppend).unwrap();
        bits.push_number_checked(4, 0).unwrap();  // first element of the sequence
        bits.push_number_checked(4, 1).unwrap();  // total length of the sequence (means 2)
        bits.push_number_checked(8, parity as usize).unwrap();  //parity of the complete data
        bits.push_byte_data(data_half).unwrap();
        bits.push_terminator(EcLevel::L).unwrap();
        assert_eq!(hex::encode(bits.clone().into_bytes()), "3013940e49207265616420746865206e657700");  // raw bytes of the first qr code of the example
    }

[RCasatta]

@kennytm any news on these?

thanks

[danieleades]

Also interested in using structured append to split a file across multiple QrCodes

[RCasatta]

@danieleades I did a fork https://github.com/RCasatta/qr_code if you are interested