Fix GradScaler import on torch >= 2.3.0

[Vectorrent]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.07%. Comparing base (d20e810) to head (f34f525).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #620      +/-   ##
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+ Coverage   85.39%   86.07%   +0.67%     
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  Files          81       81              
  Lines        8006     8014       +8     
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+ Hits         6837     6898      +61     
+ Misses       1169     1116      -53     

see 3 files with indirect coverage changes

[mryab]

Thanks for the PR! I have one small concern about compatibility, but apart from that we should be good to go

[mryab]

One small question just to make sure: if the user has torch==1.9.0 (earliest supported version in requirements.txt), does this version already have torch.amp? Maybe we need to bump the version in requirements to make sure it won't break existing code?

[Vectorrent]

This part used to exist, but got lost somewhere in splitting all of this work into multiple PRs. I've restored the logic that imports this GradScalar differently here, depending on the installed Torch version.

To answer your question, no, torch.amp does not exist in 1.9.