func (r *Reader) ReadByte() (byte, error) {
	r.prevRune = -1
	if r.i >= int64(len(r.s)) {
		return 0, io.EOF
	}
	b := r.s[r.i]
	r.i++
	return b, nil
}

// UnreadByte complements [Reader.ReadByte] in implementing the [io.ByteScanner] interface.
func (r *Reader) UnreadByte() error {
	if r.i <= 0 {
		return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
	}
	r.prevRune = -1
	r.i--