Terminates every worker thread and frees the pool.
The pool starts lazily on the first worker-mode render and lives for the life of the process, so a script that renders and exits will hang without this. A long-running server does not need it until shutdown.
WorkerCanvasis whatRootresolves to in worker mode, so a caller cannot annotate the result of their own render without it. The node types come with their factories for the same reason:Childrenis written in terms of them, and a helper returning one has to be able to say so.