Tracing for the phi model (#936)

* Add some tracing bits to mixformers.

* Add the missing file.

* Add the conv2d layer to with-tracing.

* Improve the tracing usage.

candle-transformers/src/models/mod.rs

@@ -11,4 +11,5 @@ pub mod segment_anything;
 pub mod stable_diffusion;
 pub mod t5;
 pub mod whisper;
+pub mod with_tracing;
 pub mod wuerstchen;