pr: use clap to handle help & version

[cakebaker]

This PR let's clap handle help and version, and removes the deprecated AppSettings::NoAutoHelp and AppSettings::NoAutoVersion.

[tertsdiepraam]

This is technically incompatible with GNU pr, because they don't accept -h and -v, but only the long options. I don't really mind that much in this case, though. If we want 100% compat, then we need disable_help_flag and ArgAction::Help on the custom flag (and the same for version).

[cakebaker]

Hm, at least on my machine clap doesn't use -h for help because -h is already defined for something else (the CICD / Binary sizes check, however, fails because of that).

[tertsdiepraam]

Works as a charm now! Thanks for proving me wrong :)