Analytics not functioning properly when Accept-Encoding header is set in request

Please select the area the issue is related to

Area/Management (Management API or Management Portal UI)

Please select the aspect the issue is related to

Aspect/API (API backends, definitions, contracts, interfaces, OpenAPI)

Description

Both the OpenAI and Anthropic Python and Node.js SDKs automatically include the Accept-Encoding header by default. This causes the response to be compressed, in it's current implementation token analytics are not tracked when the response is in this format.

Steps to Reproduce

1. Create a self hosted ai-gateway
2. Create an LLM provider using anthropic (any provider works)
3. Deploy LLM provider
4. Make a call to the LLM provider using postman (notice that the Accept-Encoding header is sent by default)
5. Go to the insights page on the ai workspace
6. Notice that the Completion / Prompt / Total tokens are not being tracked
7. Resend the request with the Accept-Encoding header removed
8. Notice that the Completion / Prompt / Total tokens are now being tracked

Severity Level of the Issue

Severity/Blocker (Core functionality is broken and consumer is blocked. Need immediate attention)

Environment Details (with versions)

Production, ai-gateway: v0.9.0