default <T> Callable<T> makeContextAware(Callable<T> callable) {
        return ContextAwareCallable.of(this, callable);
    }
Returns a {@link ContextAwareCallable} that makes sure the current {@link RequestContext} is
set and then invokes the input {@code callable}.
core/src/main/java/com/linecorp/armeria/common/RequestContext.java