infected_asyncio task hang (SIGINT ignored!) on debug mode breakpointing?

[goodboy]

As found in d6ed97d of the #351 work, there is a nasty issue that
causes an un-interrupt-able hang when we use enough
tractor.breakpoint()s in the right spots and infected asyncio mode
where the asyncio task somehow gets stuck in some kind of cancelled
state (maybe?)

The whole thing needs to be more thoroughly investigated and a proper
test suite built out.

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ToDo testing:

• at least one test that actually uses the flags intro-ed in
  d6ed97d with a comparable timeout.
  • a fix for that case ^ 😂