chore: add RBS

Author: mattkhan

Gemfile

@@ -25,6 +25,7 @@ gem "tzinfo-data", platforms: [:windows, :jruby]
 group :development, :test do
   # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
   gem "debug", platforms: [:mri, :windows]
+  gem "rbs", "~> 3.9.0"
 end
 
 group :development do

spec/example/sig/models/application_record.rbs

@@ -0,0 +1,2 @@
+class ApplicationRecord
+end

spec/example/sig/models/exhaustive.rbs

@@ -0,0 +1,3 @@
+class Exhaustive < ApplicationRecord
+  def model_overridden: () -> String
+end