[ARGV] No need for a separate parser file.

And rename @subject in tests to what it is.
[Banner] Consolidate related code, no more helpers.

There is no need for this indirection. It only makes it hard to know what is used where
and bad names like just ‘Helper’ should never be used again.
[Command] No need for a separate Parser module.
[ArgumentSuggester] Make it a proper class, this is a OOP language.

Making everything functions is not needed and only adds to the number of
required docs, as each argument that is passed around needs docs.
[Rubocop] Make it happy and disable a bunch of new cops.
Remove need to span multiple lines.