adds Single.never()

[hearnden]

This PR adds Single.never(), analogous to Flowable.never():

rsocket-js/packages/rsocket-flowable/src/Flowable.js

Lines 75 to 82 in bb11e45

	static never<U = empty>(): Flowable<U> {
	return new Flowable(subscriber => {
	subscriber.onSubscribe({
	cancel: emptyFunction,
	request: emptyFunction,
	});
	});
	}

[hearnden]

I also have a branch ready to turn into a PR for the corresponding change to DefinitelyTyped:

--- a/types/rsocket-flowable/Single.d.ts
+++ b/types/rsocket-flowable/Single.d.ts
@@ -47,6 +47,7 @@ export interface IFutureSubject<T> {
 export default class Single<T> {
     static of<U>(value: U): Single<U>;
     static error(error: Error): Single<never>;
+    static never(): Single<never>;
     constructor(source: Source<T>);
     subscribe(partialSubscriber?: Partial<IFutureSubscriber<T>>): void;
     flatMap<R>(fn: (data: T) => Single<R>): Single<R>;

[OlegDokuka]

@hearnden just FYI. sending nullable subscription violates reactive streams spec -> https://github.com/reactive-streams/reactive-streams-js

[OlegDokuka]

@hearnden go ahead with the PR to DT

[hearnden]

@hearnden go ahead with the PR to DT

Done: DefinitelyTyped/DefinitelyTyped#43603