Specifically after this refactoring: 5430f35

Extensions class is internal, when the library is referenced using asmdefs, Extensions class is hidden. Which results in this error:

'WaitForFrames' does not contain a definition for 'GetAwaiter' and no accessible extension method 'GetAwaiter' accepting a first argument of type 'WaitForFrames' could be found (are you missing a using directive or an assembly reference?)

Solution is to Make Extensions class public. This also means that other classes need to be made public as well:

SynchronizationContextAwaiter
IEnumeratorAwaiter
YieldInstructionAwaiter