Add Pixtral. (#2521)

* Add Pixtral.

* More pixtral vision encoder.

* Sketch a pixtral example.

* Sketch a pixtral example.

* Better image loading.

* Support loading images embedded in safetensor files.

* Clippy fixes.

* Add the llava multimodal adapter.

* Add more of the llava bits.

* Add the pixtral config.

* More pixtral inference.

* Add the text generation bits.

* Get the example to work.

* Bugfix.

* Run some bits of the model in f32.

* Blessed version :)

* Better rope frequency computations.

* README update.

candle-examples/examples/pixtral/README.md

@@ -0,0 +1,28 @@
+# pixtral
+
+Pixtral-12B is a 12B text+vision model.
+
+[Blog Post](https://mistral.ai/news/pixtral-12b/) -
+[HF Model Card](https://huggingface.co/mistralai/Pixtral-12B-2409) -
+[HF Community Model Card](https://huggingface.co/mistral-community/pixtral-12b).
+
+```bash
+cargo run --profile=release-with-debug --features cuda --example pixtral -- \
+    --image candle-examples/examples/flux/assets/flux-robot.jpg
+```
+
+```
+Describe the image.
+
+The image depicts a charming, rustic robot standing on a sandy beach at sunset.
+The robot has a vintage, steampunk aesthetic with visible gears and mechanical
+parts. It is holding a small lantern in one hand, which emits a warm glow, and
+its other arm is extended forward as if reaching out or guiding the way. The
+robot's body is adorned with the word "RUST" in bright orange letters, adding to
+its rustic theme.
+
+The background features a dramatic sky filled with clouds, illuminated by the
+setting sun, casting a golden hue over the scene. Gentle waves lap against the
+shore, creating a serene and picturesque atmosphere. The overall mood of the
+image is whimsical and nostalgic, evoking a sense of adventure and tranquility.
+```