Function build_exception_resp 

pub fn build_exception_resp<const BUF: usize>(
    out: &mut [u8; BUF],
    unit_id: u8,
    function_exception: u8,
    exception_code: u8,
) -> usize

组装异常响应：Function=03|0x80 + ExceptionCode(1) + CRC(2)