* restore to current phi modeling code from phi-2
* enable gradient checkpointing
* don't cast everything to float32 all the time
* gradient checkpointing for phi2 ParallelBlock module too
* fix enabling flash attn for phi2
* add comment about import
* fix phi2 example
* fix model type check for tokenizer
* revert float32 -> bf16 casting changes
* support fused dense flash attn
* fix the repo for flash-attn
* add package name for subdir pkg
* fix the data collator when not using sample packing
* install packaging for pytests in ci
* also fix setup to not install flash attn fused dense subdir if not extras
* split out the fused-dense-lib in extra requires
* don't train w group_by_length for phi
* update integration test to use phi2
* set max steps and save steps for phi e2e tests
* try to workaround ssave issue in ci
* skip phi2 e2e test for now
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