It is similar to what was done in #109164. I don't think it will break anything though, as the behavior remains the same?

1. This change allows base64 to support long options like --help and --decode, which is more user-friendly and standard for CLIs (e.g. base64 in Linux supports both -d and --decode).
2. It makes the usage message more helpful with colors and better formatting. It might be slightly slower than using getopt, but the trade-off is acceptable IMO.
3. Maybe there aren't any bugs now in using getopt, but I think modernizing it to use argparse will make the code more readable and easier to maintain in the future.