Provide asynchronous cleanup hooks in n-api

Editor assessment

The subject states the capability precisely: asynchronous cleanup hooks are provided in n-api. The API surface, the new mechanism, and its purpose (letting finalizers clean up asynchronously rather than synchronously) are all evident to the audience, so no body is required. The fix type is plausible for closing a functional gap, though feat would fit equally, and the straddle is not penalized. No scope is attached, no footers appear, and hygiene is clean. The message communicates a real API-behavior improvement in one accurate line.