StreamClass.into<S>(source: Source<S>,sink: WritableStream<Exclude<S, AnyFailure>>): StreamClass<Exclude<S, AnyFailure>, Extract<S, AnyFailure>>
StreamClass#into as a static: Stream.into(source, …) is
Stream.from(source).into(…).
await Stream.into([1, 2], new WritableStream()).collect(); // [1, 2]
sink: WritableStream<Exclude<S, AnyFailure>>
StreamClass<Exclude<S, AnyFailure>, Extract<S, AnyFailure>>