test: avoid missing worker exit events

[GrapeBaBa]

Motivation

The worker lifecycle test waited for the worker message before registering its exit listener. Node can drain a queued message and emit exit in the same turn, causing the test to miss the exit event and time out intermittently in CI.

Description

• Register the worker message and exit listeners before yielding.
• Await both events together with node:events once(), which also propagates worker errors.
• Assert a successful worker exit and check the restored refcount without an arbitrary delay.

Validated by running the worker lifecycle suite 50 consecutive times.