Phi-3 conversation format, example training script and perplexity metric (#1582)

* phi-3 support and perplexity metric

* phi-3 chat template

* metrics updates

* chore: lint

* fix assertion on Tensor

* fix tests since tokenization happens in the metric

* fix perplexity value of shorter passage

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Co-authored-by: Wing Lian <wing.lian@gmail.com>

.gitignore

@@ -176,3 +176,9 @@ qlora-out/*
 mlruns/*
 
 /.quarto/
+prepared-datasets/
+submit.sh
+*.out*
+
+typings/
+out/