SseEventOutputImpl should not log and throw

SseEventOutputImpl#writeEvent() catches exceptions, logs them, then rethrows them. IMO this is a bad idea. You often don't know that the underlying channel is dead until you try to write to it, which results in useless log spam. Also, log-and-throw is an anti-pattern, and the send future will get completed with the exception anyway, so it should be the application's responsibility to check the outcome and log if it wants to.