[BUG] HttpAsyncClientBuilder.defaultIOReactorConfig gets overwritten by default RestClientBuilderCustomizer

[nstdio]

What is the bug?

Cannot configure HttpAsyncClientBuilder.defaultIOReactorConfig using RestClientBuilderCustomizer because default customizer overwrites it.

How can one reproduce the bug?

Define a RestClientBuilderCustomizer and configure HttpAsyncClientBuilder.defaultIOReactorConfig and see that it does not have effect.

What is the expected behavior?

To user defined RestClientBuilderCustomizer have effect regarding HttpAsyncClientBuilder.defaultIOReactorConfig.

What is your host/environment?

Java: 21.0.5+11
Spring Data OpenSearch: 1.5.4
Spring Boot: 3.3.6

Do you have any additional context?

I've tried to use @Order to force my customizer be applied last (by the way overwriting whatever changes were made by default customizer), but default one does not define any order so it'll come as lowest precedence.