Improve `to_s`/`inspect`/`to_yaml`

[raghubetina]

It would be nice to improve to_s/inspect/to_yaml on Chat so that it's easier to see the message list as it grows, when using pp, puts, ap, and/or <%= debug(chat) %>

https://guides.rubyonrails.org/v8.0/debugging_rails_applications.html#debug