Remove integration spec file & private method test

- Specs are all moved to their own files!
- The remaining tests were unit tests on the
  `meilisearch_settings_changed?` method which should be tested but not
  this way. Postponing until the logic has been refactored out of the
  MeiliSearch::Rails module.
- Do not require every ActiveRecord table in every test
  - Some require statements that were missing were added in this commit

Author: ellnix

spec/integration_spec.rb

@@ -3,6 +3,8 @@
 require 'support/models/book'
 require 'support/models/animals'
 require 'support/models/people'
+require 'support/models/vegetable'
+require 'support/models/fruit'
 require 'support/models/disabled_models'
 require 'support/models/queued_models'
 

spec/options_spec.rb

@@ -159,6 +159,7 @@
     let(:public_songs_index) { safe_index_uid('Songs') }
 
     it 'targets multiple indexes' do
+      Song.clear_index!(true)
       songs =
         [
           Song.create!(name: 'Coconut nut', artist: 'Smokey Mountain', premium: false, released: true),