StreamClass.intersperse<S, Sep>(source: Source<S>,separator: Sep): StreamClass<Exclude<S, AnyFailure> | Sep, Extract<S, AnyFailure>>
StreamClass#intersperse as a static: Stream.intersperse(source, …) is
Stream.from(source).intersperse(…).
await Stream.intersperse([1, 2], 0).collect(); // [1, 0, 2]
StreamClass<Exclude<S, AnyFailure> | Sep, Extract<S, AnyFailure>>