.Net: Bug: Chatcompletion usage object reflects only last LLM call even when multiple has been made

[AlesRuzickaEu]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Perform IChatCompletionService.GetChatMessageContentAsync
2. Extract usage object (for example for OpenAI)
3. Check Token count
4. Token count is just last API call, which can be fraction of reality

Expected behavior
I expect usage object that sums all OpenAI api calls for proper accounting

Platform

• Language: C#
• Source: NuGet package 1.54.0
• AI model: OpenAI:GPT-4o-mini

Additional context
To have proper accounting of tokens spend per customer, it is a must to be able to get to proper token count somehow