Asynchronous context manager for managing groups of tasks.
Example use:
async with asyncio.TaskGroup() as group:
task1 = group.create_task(some_coroutine(...))
task2 = group.create_task(other_coroutine(...))
print("Both tasks have completed now.")
All tasks are awaited when the context manager exits.
Any exceptions other than `asyncio.CancelledError` raised within
a task will cancel all remaining tasks and wait for them to exit.
The exceptions are then combined and raised as an `ExceptionGroup`.