Disable Style/OneClassPerFile

Newer RuboCop releases activated Style/OneClassPerFile by default,
which flags two intentional patterns in this codebase:

- The ActiveRecord::Associations::Preloader::Association reopen in
  lib/simple_master.rb, which is a monkey-patch and not a new class.
- STI subclass families colocated in a single model file in the
  rails_sample.

Both patterns are deliberate, so disable the cop project-wide.

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