Convert compatible prelu weights to rank 1

[laggui]

Checklist

• Confirmed that run-checks all script has been executed.

Related Issues/PRs

Fixes #2053

Changes

PRelu alpha weights can have rank > 1. This PR converts compatible weights to rank 1.

Testing

Model in linked issue works.

[antimora]

LGTM!

Thanks for fixing it!

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.

Project coverage is 86.43%. Comparing base (4c73532) to head (74d3af5).

Files	Patch %	Lines
crates/burn-import/src/onnx/to_burn.rs	44.44%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2054      +/-   ##
==========================================
- Coverage   86.43%   86.43%   -0.01%     
==========================================
  Files         683      683              
  Lines       87245    87253       +8     
==========================================
+ Hits        75410    75413       +3     
- Misses      11835    11840       +5     

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