docs: public static <V> Supplier<V> retryable(Supplier<V> base,
                                            Class<? extends Throwable> exceptionClass,
                                            int maxRetries,
                                            int maxDelayBetweenRetries) {
      return () -> new RetryingFunction<>(v -> base.get(),
          exceptionClass,
          maxRetries,
          maxDelayBetweenRetries).apply(null);
    }