Controller for task admission

[mr-chelyshkin]

📝 Description

Add new feature object: controller which can manage task admission with a few rules:

• Skip task if already running.
• Stop current task and start new one immediately.
• Queue the task (FIFO order).

🔄 Related Issues

Resolves #39 (if applicable)

✅ Checklist

• Documentation updated (README, rustdoc, examples)
• Tests added/updated (if relevant)
• No breaking changes introduced
• CI passes locally

📸 Screenshots / Logs (if applicable)

// Supervisor as a Builder
let sup = Supervisor::builder(Config::default())
        .with_subscribers(vec![Arc::new(LogWriter::default())])
        .with_controller(ControllerConfig::default())
        .build();
        
// New wrapper example
sup.submit(ControllerSpec::queue(my_awesome_worker)).await?
sup.submit(ControllerSpec::replace(my_awesome_worker)).await?;