Updated task tests: working with non-synchronous backends.

[isoos]

• Apparently these work with both almost-sync backends (current HEAD) and also with Check which tests are fragile / depend on timing. #9069.
• In most cases the change only tracks/awaits the creation of the cloud worker instance, but for some tests I needed to modify the assertion logic too.
• Note: I think we should rewrite the scheduling logic and its async delegation (which is implemented with scheduled microtasks), exposing more control and also some event over it, in order to make these tests more readable.

[jonasfj]

What if you did:

await Future.wait([
  created,
  await clockControl.elapse(minutes: 5),
]);

[isoos]

Note: I've checked how these are behaving with the wip-typed-sql rewrite, and it now passes 5 tests out of 8, and 2 of the 3 failing is probably related to scheduling.

Before going further with this, I'll look into the ControlledClock as we've discussed offline.