Tests for happy eyeballs + working around bug in wait_for

[twisteroidambassador]

Bug report

The happy eyeballs implementation in asyncio is potentially affected by #86296 , i.e. where asyncio.wait_for may swallow cancellation.

I have added some tests for this particular problem, and some more tests for other aspects of happy eyeballs, because I didn't write any when first contributing the implementation. My bad.

The current PR only contains the tests. I'll do the actual fix later.

Linked PRs

• GH-98388: Add tests for happy eyeballs and its internal workings #98389