Add support for a form of `when_all`

[kammce]

This issue will contain the list of tasks and utilities required to implement concurrent operations in a single thread.

co_await hal::cooperative_when_all(driver1->api1(ctx1), driver2->api2(ctx2), driver3->api3(ctx3));

This would perform a cooperative round robin execution of all of the coroutines then suspends itself. When resumed it will perform the cooperative round robin execution again until all coroutines have finished, then it will return.

This and the libraries that are coming from sender/receivers should make up what we need. This issue is for adding additional APIs beyond whats available.

[kammce]

We can also see if sender/receivers are a good fit for this with std::exec::when_all, but we'd need to test.