Support ruby 3.0 and Rails < 7

[alvaromat]

Hi. First of all thanks for all your work.

I've seen ruby 3 is not supported because it's reached EOL.
We are still using ruby 3.0. I acknowledge we need to upgrade, but having a large monolith is not a trivial task for us.
We are using this gem on version 0.9.3, as it's the last one that doesn't require ruby 3.1.

Does the gem need to force to use ruby 3.1? The result for us, and I guess many other people, is that we are forced to use an old version of langchainrb until we upgrade ruby.

We have also a conflict with ActiveSupport. Is ActiveSupport version 7 needed? This dependency prevents to use the gem on Rails < 7