[AsyncStreaming] The expected behavior of `ConcludingAsyncReader.consumeAndConclude`'s body returning without reading to the end

If `ConcludingAsyncReader.consumeAndConclude`'s body returns without reading to the end, before the final element is read. What should we do?

1. Keep reading to the end: not ideal since it can leak the resource.
2. Throw an error: conflict with typed throws.
3. Implementation-specific behavior, potentially returning a different value as the final element.