Add support for namespaced Devise models in views path

[losingle]

This commit modifies the add_devise_routes method to handle namespaced Devise models correctly. When the class_name includes a namespace (i.e., contains "::"), the namespace is used as the as option value for the devise_for route helper. This ensures that Devise looks for views in the correct directory corresponding to the namespace of the model. https://github.com/heartcombo/devise/blob/f6e73e5b5c8f519f4be29ac9069c6ed8a2343ce4/lib/devise/mapping.rb#L55