LM Studio doesn't show the context token wheel (#53790) because token
usage is
never reported in streaming responses.

Causes:

1. `stream_options` was missing from the request. Without
`stream_options: { include_usage: true }`, the LM Studio API omits
`usage`
   from every streaming chunk entirely.

2. The event mapper discarded usage data in the final chunk.
OpenAI-compatible
servers send the usage summary in a trailing chunk that has an empty
`choices`
array. The old guard treated that as an error, so even when usage was
present
   it was thrown away before emitting a `UsageUpdate` event.

Fix:
- Add `StreamOptions { include_usage: bool }` and `stream_options` to
`ChatCompletionRequest`, and always set it to `true` for streaming
requests.
- Move usage handling in `LmStudioEventMapper::map_event` to run
*before* the
  empty-choices guard, mirroring the OpenAI provider's approach.
- Add four unit tests for `map_event` covering the fixed behavior.

Release Notes:

- Fixed LM Studio not showing the context window usage wheel. 

<img width="1184" height="1080" alt="Screenshot_20260527_130449"
src="https://github.com/user-attachments/assets/97eb8500-39dd-4824-aaf8-f0422b62119d"
/>

---------

Co-authored-by: Gabriele Ancillai <gabriele.ancillai@sofka.com.co>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>