Such that when `maybe_context.cancel()` is not called (explicitly) and
only the subactor is cancelled by its parent we expect to see a ctxc
raised both from any call to `Context.wait_for_result()` and out of
the `Portal.open_context()` scope, up to the `trio.run()`.
Deats,
- obvi call-n-catch the ctxc (in scope) for the oob-only
subactor-cancelled case.
- add branches around `trio.run()` entry to match.
Discovered while writing a `@context` sanity test to verify unmasker
ignore-cases support. Masked code is due to the process of finding the
minimal example causing the original hang discovered in the original
examples script. Details are in the test-fn doc strings and surrounding
comments; more refinement and cleanup coming obviously.
Also moved over the self-cancel todos from the inter-peer tests module.
Tyler Goodlet