Reports classes that directly implement the Subscriber interface.

Consider using static generators from RxJava, Reactor or Mutiny, for example:

• Flux.just(), Flux.create(), Flux.generate(), Flux.from()
• Mono.create(), Mono.from(), Mono.just()
• Flowable.just(), Flowable.from()
• Maybe.just(), Maybe.from()
• Multi.createFrom(), Multi.createBy()
• Uni.createFrom()