add base64 dependancy when using ruby 3.3 or greater

[mmenanno]

This is a reopening of the PR that I accidentally closed here #107

I now have it as a conditional based on the ruby version so that we only inject the dependency manually when on the ruby versions that require it.

[Earlopain]

This condition will not work, depending on the ruby version used to build/publish the gem it will either declare the dependency or not do that, for all ruby versions used to run it. I have my doubts about the possibility of a new release, just wanted to let you know.

Since the first released version of base64 is Ruby >= 2.3.0, it will also implicitly raise required_ruby_version

[mmenanno]

Hmmm to you think it would make sense then for me to remove the condition and bump the required_ruby_version of this gem to >= 2.3.0? And then if we happen to be able to get another release of the gem that should fit the bill?

[Earlopain]

Yes. Alternatively, replace the one base64 call being done in this gem with the unpack equivalent and remove base64 requires:

# Equivalent to Base64.decode64
def self.base64_decode(input)
  # TODO: Condition can be droped if Ruby >= 2.4.0
  if input.respond_to?(:unpack1)
    input.unpack1('m')
  else
    input.unpack('m').first
  end
end