[11.x] Execute event listener using Fiber

[robertogallea]

Summary
This PR introduces the ability to execute Event Listeners using PHP Fibers. This enhancement can significantly improve performance, especially when the sync driver is used for event dispatching.

How it works
To leverage this feature, a Listener class simply needs to include the RunsOnFiber trait—no additional setup required. The event dispatcher automatically detects listeners using this trait and executes their handling logic inside a Fiber. The RunsOnFiber trait provides a built-in decorator to handle the execution seamlessly.

This approach ensures a lightweight integration of Fibers, offering better responsiveness and concurrency for event-driven workflows.

[taylorotwell]

Please provide before and after benchmarks in a real world scenario. 👍 Thanks!