delegate type that can be used as a fiber
function type that can be used as a fiber
acts like a std.thread.Fiber - adds child Fiber member to enable yield on child fibers (=wait for child fiber to finish)
returns a function object that can be used to wait in a UEFiber for a certain amount of time
UEFibers acts as a container for fibers. It manages reusing UEFiber objects after they are finished. startFiber first tries to find a finished UEFiber and only otherwise allocates