Add csv gem to gemspec

[davidarendsen]

Got a warning that csv will no longer be part of the default gems since Ruby 3.4.0.
So this needs to be added in the gemspec.

[rafbm]

It seems CSV is only used for a one-time parse of digits.csv which looks like it could easily be converted to YAML. Would there be interest in such conversion to avoid the CSV dependency?

[davidarendsen]

I could convert it to a YAML file and make that work.
However I see that the CSV's content was generated by a script that I don't see in the repository. So not sure how often this would change. When a change is required that script should also be changed.

# Built with script/development/generate_digits_characters.rb
def read_digits
  File.read("#{__dir__}/data/digits.csv")
end