Fix Issue JSONAPI-Resources#1464: Rails 7.1 Zeitwerk autoloading race condition

Issue JSONAPI-Resources#1464 reported intermittent 'NameError: uninitialized constant
JSONAPI::ResourceController' errors in Rails 7.1 when eager_load is disabled.

Root cause:
- ActiveSupport.on_load(:action_controller_base) lazy loading mechanism
- Causes race condition with Zeitwerk autoloading in Rails 7.1+
- Errors occur randomly during test execution
- Only happens locally, not in CI with eager loading enabled

Solution:
- Remove conditional lazy loading with ActiveSupport.on_load
- Always require 'jsonapi/resource_controller' directly
- Eliminates race condition with Zeitwerk

The fix ensures ResourceController is always available without
depending on ActionController::Base load timing.

Workarounds no longer needed:
- config.eager_load = true in test environment
- Manual require 'jsonapi/resource_controller' before use
- Switching to ActsAsResourceController mixin

Related: https://github.com/cerebris/jsonapi-resources/issues/1464

Author: takaokouji

lib/jsonapi-resources.rb

@@ -9,13 +9,10 @@
 require 'jsonapi/cached_response_fragment'
 require 'jsonapi/response_document'
 require 'jsonapi/acts_as_resource_controller'
-if Rails::VERSION::MAJOR >= 6
-  ActiveSupport.on_load(:action_controller_base) do
-    require 'jsonapi/resource_controller'
-  end
-else
-  require 'jsonapi/resource_controller'
-end
+# Load resource_controller directly to avoid Zeitwerk autoloading issues in Rails 7.1+
+# Previously used ActiveSupport.on_load which caused race conditions with Zeitwerk
+# See: https://github.com/cerebris/jsonapi-resources/issues/1464
+require 'jsonapi/resource_controller'
 require 'jsonapi/resource_controller_metal'
 require 'jsonapi/resources/version'
 require 'jsonapi/configuration'