#1901 test: synchronize the keepawake service fixture

Descripción

The synchronous mock request can finish before the asynchronous keepawake worker runs. The service test then waits for an ON/OFF pair that the worker never needed to emit, causing an intermittent assertion failure.

Keep the mock request generator open until the fake Windows call records ON, then finish it and check OFF. Register cleanup for both request generators and the worker so failed assertions also release them. This changes only the test fixture; the runtime's keepawake behavior is unchanged.

Validation on upstream main `61b3fb5d`: the original test fails deterministically when an event barrier delays the worker until after the mock request ends. The corrected fixture passes five runs with that controlled ordering, and all six keepawake tests pass. The real Windows power API was forbidden throughout; no model was loaded and no actual suspend/resume behavior is claimed.