Use `ActiveSupport.on_load` to defer autoloaded Action Cable constants

[bensheldon]

This wraps autoloaded Action Cable constants with on_load hooks to ensure they are deferred and speed up application boot:

• https://api.rubyonrails.org/classes/ActiveSupport/LazyLoadHooks.html
• https://island94.org/2024/07/on-the-importance-of-rails-code-reloading