Add token usage to streamed chat

Problem/Motivation

Currently we have the possibility to abstract token usage for anyone using normal static chat, see ✨ Abstract token usage Active , however for the streamed chat message this will not happen, since we do not know token usage until the final chunk is strreamed.

We need to add this to the PostStreamingResponseEvent as well.

Steps to reproduce

Proposed resolution

• Add so that you can collect tokens in the StreamedChatMessage, but do not add it to the interface (no breaking changes).
• Add so we can collect it in the PostStreamingResponseEvent
• Add so we inject it into the PostStreamingResponseEvent, but not in the constructor (no bkreaing changes)

Remaining tasks

User interface changes

API changes

Data model changes