feat: expose GPU energy consumption (mJ) in responses

# What does this PR do? This PR adds **energy consumption measurement** to each request served by the router. A new field `energy_mj` (in millijoules) is added to the `details` section of the response. Example usage: ```bash curl 127.0.0.1:3000/generate \ -X POST \ -d '{"inputs":"What is Deep Learning?","parameters":{"max_new_tokens":20, "details":true}}' \ -H 'Content-Type: application/json' ``` Response (excerpt): ```json { "generated_text": "Deep learning is a subset of machine learning...", "details": { "finish_reason": "length", "generated_tokens": 20, "tokens": [...], "energy_mj": 108836 } } ``` ### Motivation * Provide users with direct insight into the **energy usage** of their requests. * Enable frontends (e.g. [[Chat UI Energy Demo](https://huggingface.co/spaces/jdelavande/chat-ui-energy)](https://huggingface.co/spaces/jdelavande/chat-ui-energy)) to display this metric alongside generated text. * Support sustainability efforts by making energy costs more transparent. ### Limitations * The measurement is taken at the **GPU level** during the full processing of the request by the router. * Energy is **not attributed per user** when multiple requests are batched — values represent an approximation of total GPU energy consumption. * Despite this, the metric remains useful to give users an idea of the energy footprint of their queries without deploying TGI themselves. --- ## Before submitting * [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case). * [x] Did you read the [[contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests)](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests), Pull Request section? * [ ] Was this discussed/approved via a Github issue or the [[forum](https://discuss.huggingface.co/)](https://discuss.huggingface.co/)? Please add a link to it if that's the case. * [ ] Did you make sure to update the documentation with your changes? Here are the [[documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs)](https://github.com/huggingface/transformers/tree/main/docs), and [[here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation)](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation). * [x] Did you write any new necessary tests? --- ## Who can review? @regisss @Narsil