To make the recent set of tests pass this (hopefully) finally solves all
`asyncio` embedded `trio` guest-run abandonment by ensuring we "pump the
event loop" until the guest-run future is fully complete.
Accomplished via simple poll loop of the form `while not
trio_done_fut.done(): await asyncio.sleep(.1)` in the `aio_main()`
task's exception teardown sequence. The loop does a naive 10ms
"pump-via-sleep & poll" for the `trio` side to complete before finally
exiting (and presumably raising) from the SIGINT cancellation.
Other related cleanups and refinements:
- use `asyncio.Task.result()` inside `cancel_trio()` since it also
inline-raises any exception outcome and we can also log-report the
result in non-error cases.
- comment out buncha not-sure-we-need-it stuff in `cancel_trio()`.
- remove the botched `AsyncioCancelled(CancelledError):` idea obvi XD
- comment `greenback` init for now in `aio_main()` since (pretty sure)
we don't ever want to actually REPL in that specific func-as-task?
- always capture any `fute_err: BaseException` from the `main_outcome:
Outcome` delivered by the `trio` side guest-run task.
- add and raise a new super noisy `AsyncioRuntimeTranslationError`
whenever we detect that the guest-run `trio_done_fut` has not
completed before task exit; should avoid abandonment issues ever
happening again without knowing!
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