Forego kotlinx-coroutines interception

[kyay10]

Interception slows down a lot of tests, and it's unnecessary since we don't switch coroutines. We could implement a simple trampolining implementation, but we should keep in mind that using delay or launch will still intercept our continuation, and so we should also implement a custom ContinuationInterceptor that runs the trampoline (I think we previously had a custom Interceptor for other reasons, so we can repurpose that).