Set devices to 1 if multi-gpu is configured

[samet-akcay]

📝 Description

• Multi-GPU is currently not supported in anomalib due to how metrics are handled. This PR checks if user passes multi-gpu configuration and properly re-configures to single GPU with correct GPU id .

✨ Changes

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• 🐞 Bug fix (non-breaking change which fixes an issue)
• 🔨 Refactor (non-breaking change which refactors the code base)
• 🚀 New feature (non-breaking change which adds functionality)
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• 📚 Documentation update
• 🔒 Security update

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[codecov]

Codecov Report

Attention: Patch coverage is 32.43243% with 25 lines in your changes missing coverage. Please review.

Project coverage is 80.64%. Comparing base (cfd3d8e) to head (6eebcc1).
Report is 3 commits behind head on main.

Files	Patch %	Lines
src/anomalib/engine/engine.py	32.43%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2256      +/-   ##
==========================================
- Coverage   80.80%   80.64%   -0.17%     
==========================================
  Files         248      248              
  Lines       10859    10894      +35     
==========================================
+ Hits         8775     8785      +10     
- Misses       2084     2109      +25     

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[ashwinvaidya17]

What happens if someone passes devices =2? If I am not wrong, it will still start distributed training.

[samet-akcay]

Good catch! I've added few more logic to cover some other edge cases.

[samet-akcay]

Closing as this for the sake of #2435