Extended lifetime shared workers

This feature introduces the extendedLifetime option for the SharedWorker constructor. It allows a shared worker to stay alive for a short period after all connected clients (e.g., pages) have been unloaded. This is useful for performing asynchronous tasks that need to complete after a page unloads, such as saving data to IndexedDB or sending analytics. Currently, this requires a Service Worker, which can be heavyweight for this use case. This origin trial provides a more lightweight alternative.