Replace `client.rb` with ruby-client gem

We're using an (outdated) copy of api client code from the ruby-client repo.

When we're stable enough, and ruby-client is packaged as a gem, we should replace `client.rb` with the gem.

Depends on the state object extraction in #48

Start by reviewing client.rb, the ruby-client repository or gem packaging status, and the state object extraction tracked in issue #48. Confirm that the gem is available and that #48 is complete before replacing the copied client code. Done means client.rb is replaced by the ruby-client gem without retaining the outdated copy.

Written by the indexing model from the issue text.