Tests fail with the iOS simulator

[twittemb]

The unit tests fail when being run on the iOS simulator. I think we already had this conversation and it might be related to the fact that the iOS simulator cannot spawn concurrent tasks because of the numbers of core.

@phausler As you are planning a v1.0 soon, I was wondering if we should make sure the tests are OK (if this is even possible) on every platform ?

[FranzBusch]

The iOS simulator can spawn concurrent tasks but it is limited to a cooperative pool size of 1 as far as I am aware. This surfaces some issues where code is assuming that stuff is run in parallel. We should definitely check the code paths that hit this and fix them up because Swift Concurrency expects forward progress on any active task and if that is not possible the task should suspend.