FSDP2 + LoRA kernels (#2992)

* impl fix

* smoke tests

* patches for fsdp2 + qlora compat

* nit

* working fix

* working fix

* fix merge

* minifying patches; update bnb dep

* renaming; adding tests

* remove duplicate test, add dora guard

* generalize __torch_function__

* revert generalization

* update comments

requirements.txt

@@ -1,7 +1,7 @@
 --extra-index-url https://huggingface.github.io/autogptq-index/whl/cu118/
 
 # START section of dependencies that don't install on Darwin/MacOS
-bitsandbytes==0.46.0
+bitsandbytes==0.46.1
 triton>=3.0.0
 mamba-ssm==1.2.0.post1
 xformers>=0.0.23.post1