Add sign ONNX op import support

[wufniks]

Pull Request Template

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

Related Issues/PRs

I couldn't find one.

Changes

Added sign ONNX op import support

Testing

Added unit tests for codegen and expected outputs

[antimora]

Looks great! Thanks for adding this op!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.42%. Comparing base (9fbcbed) to head (6ee6ef7).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1663   +/-   ##
=======================================
  Coverage   86.41%   86.42%           
=======================================
  Files         694      694           
  Lines       80675    80716   +41     
=======================================
+ Hits        69719    69760   +41     
  Misses      10956    10956           

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