Integrate PEFT LoRA with HuggingFaceModel

[dakinggg]

This PR integrates PEFT LoRA with the HuggingFaceModel base class.

Manual test (requires a Foundry PR also), comparing the current lora implementation on foundry main (no fsdp), this implementation (no fsdp), and this implementation (with fsdp)

TODO:

• rerun lora test (after refactor) mpt-7b-lora-after-fsdp-14-vcRBaL
• rerun non lora test (without peft installed, after refactor) no-lora-after-3-ObUYGR
• test that a small checkpoint shows up in object store mpt-7b-lora-after-fsdp-14-vcRBaL

[irenedea]

LGTM! thanks for adding the tiny mistral fixtures and better typing throughout!

[mvpatel2000]

Does the huggingface class actually need to be in Composer? I suppose it's a useful general utility...

1 minor nit. I think this makes sense otherwise