@Nonnull
    static <T extends Event> SingleSubscriptionBuilder<T> newBuilder(@Nonnull Class<T> eventClass, @Nonnull EventPriority priority) {
        Objects.requireNonNull(eventClass, "eventClass");
        Objects.requireNonNull(priority, "priority");
        return new SingleSubscriptionBuilderImpl<>(eventClass, priority);
    }
Makes a HandlerBuilder for a given event

@param eventClass the class of the event
@param priority   the priority to listen at
@param <T>        the event type
@return a {@link SingleSubscriptionBuilder} to construct the event handler
@throws NullPointerException if eventClass or priority is null
helper/src/main/java/me/lucko/helper/event/functional/single/SingleSubscriptionBuilder.java