Composite tasks do not notify parent composites

WhenAllTask and WhenAnyTask mark themselves complete, but do not notify their parent composite.

This means the following orchestration does not resume when all activities complete:

all_task = task.when_all(activity_tasks)
winner = yield task.when_any([cancel_task, all_task])

A current workaround is to wait for each leaf task with repeated when_any calls. The workaround preserves cancellation, but Durable Task Scheduler no longer shows the standard Fan-out group.

Could composite completion propagate to the parent in the same way that CompletableTask.complete() does?

A regression test can compose when_any([cancel, when_all([a, b])]), complete a and b, and verify that the outer task completes with the inner when_all task.

まず WhenAllTask と WhenAnyTask を読み、それらの完了動作を CompletableTask.complete() と比較します。issue で説明されている when_any([cancel, when_all([a, b])]) の回帰テストを追加します。done とは、a と b を完了させることで外側の task が内側の when_all task とともに完了することを意味します。