4.15.1 raises the typing_extensions requirement marker from
python_version < "3.13" to < "3.15", so it is now a real runtime
dependency on python 3.14 and importing anyio fails without it.
Add python3-typing-extensions to DEPENDS.
Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>
Exercise anyio end-to-end with the structured-concurrency example
from the upstream "Creating and managing tasks" docs: spawn 5 child
tasks via create_task_group(), each appending to a shared list, then
verify all completed.
Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>