Force deepchat question/reply to be 1 trace

Problem/Motivation

This is a pretty complex one - deepchat breaks down a single interaction into multi-ajax requests.

So far Langfuse treated 1 drupal lifecycle as 1 request. And deepchat forces us to change that.
We would need to introduce multiple changes to the SDK to make it work properly, non-breaking changes (add serialization, a few setters, etc).

Keeping 1 single interaction: Question / Reply as 1 single trace will make the tracing way more understandable.

Steps to reproduce

Use deepchat - use an assistant that can delegate a task to another agent - you will see that it will break the trace into 2 logged traces.