static CircuitBreakerClientHandler of(CircuitBreaker circuitBreaker) {
        requireNonNull(circuitBreaker, "circuitBreaker");
        return of((ctx, req) -> circuitBreaker);
    }
Creates a default {@link CircuitBreakerClientHandler} which uses the provided
{@link CircuitBreaker} to handle requests.
core/src/main/java/com/linecorp/armeria/client/circuitbreaker/CircuitBreakerClientHandler.java