Finally this reproduces the issue as it (originally?) exhibited inside
`piker` where the `Actor.lifetime_stack` wasn't closed in cases where
during `infected_aio`-actor cancellation/shutdown `trio` side tasks
which are doing shielded (teardown) work are NOT being watched/waited on
from the `aio_main()` task-closure inside `run_as_asyncio_guest()`!
This is then the root cause of the guest-run being abandoned since if
our `aio_main()` task-closure doesn't know it should allow the run to
finish, it's going to call `loop.close()` eventually resulting in the
`GeneratorExit` thrown into `trio._core._run.unrolled_run()`..
So, this extends the `test_sigint_closes_lifetime_stack()` suite to
include cases for such shielded `trio`-task ops:
- add a new `trio_side_is_shielded: bool` which will toggle whether to
add a shielded 0.5s `trio.sleep()` loop to `manage_file()` which
should outlive the `asyncio` event-loop shutdown sequence and result
in an abandoned guest-run and thus a leaked file.
- parametrize the existing suite with this case resulting in a total 16
test set B)
This patch demonstrates the problem with our `aio_main()` task-closure
impl via the now 4 failing tests, a fix is coming in a follow up commit!
f090bf32f2