Disable DSD and fix bitsandbytes test

[RdoubleA]

Context

What is the purpose of this PR? Is it to

• add a new feature

• fix a bug

• update tests and/or documentation

• other (please add here)

• Temporarily disable DSD until we resolve Revert DSD to fix breakages #2313 and Llama3.2 vision does not run with distributed state dict #2277

• Only import bitsandbytes when CUDA is available in NF4 linear tests, otherwise it fails trying to setup CUDA. Not sure if this was a recent change to BNB.

Changelog

What are the changes made in this PR?
*

Test plan

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[pytorch-bot]

🔗 Helpful Links

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⏳ No Failures, 1 Pending

As of commit 9c5fac8 with merge base d4465c8 ():
💚 Looks good so far! There are no failures yet. 💚

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.64%. Comparing base (46d8153) to head (75fe084).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2314       +/-   ##
===========================================
+ Coverage   23.87%   66.64%   +42.77%     
===========================================
  Files         359      354        -5     
  Lines       21260    20731      -529     
===========================================
+ Hits         5076    13817     +8741     
+ Misses      16184     6914     -9270     

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[ebsmothers]

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