### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

Calling `POST /utils/transform_request` can prevent the proxy worker from responding to unrelated requests, including `/health/liveliness`, until the provider call finishes

The async route calls the synchronous `return_raw_request()` directly on the event-loop thread. When request transformation waits for provider I/O, other coroutines on the same worker cannot run

Expected behavior: waiting for the provider during `/utils/transform_request` must not block the proxy event loop or delay unrelated requests such as `/health/liveliness`

Whether `/utils/transform_request` should contact the provider is outside the scope of this issue

### Steps to Reproduce

1. Check out commit `0fbdea4bf5` and start the proxy with `allow_client_side_credentials: true` 2. Point `api_base` at an OpenAI-compatible endpoint that waits one second before returning 401 3. Start a transform request, then send a health check 50 ms later

~~~shell time curl -s http://localhost:4000/utils/transform_request \ -H "Authorization: Bearer $LITELLM_MASTER_KEY" \ -H "Content-…