StreamClass.tap<S>(source: Source<S>,fn: (value: Exclude<S, AnyFailure>,index: number) => void | PromiseLike<void>): StreamClass<Exclude<S, AnyFailure>, Extract<S, AnyFailure>>
StreamClass#tap as a static: Stream.tap(source, …) is
Stream.from(source).tap(…).
await Stream.tap([1, 2], () => {}).collect(); // [1, 2]
StreamClass<Exclude<S, AnyFailure>, Extract<S, AnyFailure>>