Add the Qwen2 model (#1684)

* Initial check-in for the qwen2 model.

* More qwen2 inference.

* Polish the qwen example.

* Fix the rope basis.

* Get the inference to work.

* Support different model sizes.

candle-transformers/src/models/mod.rs

@@ -30,6 +30,7 @@ pub mod quantized_mixformer;
 pub mod quantized_mpt;
 pub mod quantized_stable_lm;
 pub mod quantized_t5;
+pub mod qwen2;
 pub mod repvgg;
 pub mod resnet;
 pub mod segment_anything;