Adopt SLF4J instead of Java Util Logging

[edeandrea]

Discussed in #91

^{Originally posted by ThomasVitale November 23, 2025}
@edeandrea @lordofthejars just thinking about whether we should adopt SLF4J in the project. I realised now we are using Java Util Logging.

Personally, I'm fine either way. But from a contribution perspective, SLF4J is more broadly used in Java libraries so it might be more familiar to contributors. For example, LangChain4j uses SLF4J as well.

What do you think?