Address newer RuboCop offenses surfaced on CI

Newer RuboCop releases (resolved by CI via bundler-cache) activated
cops not present when v1.0.0 was released. The two offenders here are
unrelated to the marshal-loader change but block CI on this branch:

- Disable Style/OneClassPerFile in .rubocop.yml. Both the AR preloader
  monkey-patch in lib/simple_master.rb and the STI subclasses in the
  rails_sample models intentionally pack related declarations.
- Realign the inner-block indentation in queryable.rb so the closing
  brace and the if/else body share the same anchor.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: AZQ1994

.rubocop.yml

@@ -60,6 +60,9 @@ Style/Lambda:
 Style/MultilineBlockChain:
   Enabled: false
 
+Style/OneClassPerFile:
+  Enabled: false
+
 Style/StringLiterals:
   Enabled: false
 

lib/simple_master/master/queryable.rb

@@ -42,7 +42,7 @@ def insert_queries(records, on_duplicate_key_update = false, batch_size: 10000)
                   else
                     record.send(method_name)
                   end
-              }.join(", ").then { "(#{_1})" }
+                }.join(", ").then { "(#{_1})" }
             }.join(", \n")
 
           "INSERT INTO `#{table_name}` \n#{sql_columns} VALUES \n#{values_sql}#{on_duplicate_key_update_sql};\n"