fix: efficient ad model_size str fixes

[Gornoka]

📝 Description

• imprved handling of efficient ad model_size Enum handling
• 🛠️ Fixes [Bug]: Issue with self.model_size Initialization in EfficientAD Class #2157

✨ 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)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔒 Security update

✅ Checklist

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[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 80.78%. Comparing base (56843d2) to head (1ae5637).
Report is 5 commits behind head on main.

Files	Patch %	Lines
...malib/models/image/efficient_ad/lightning_model.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2159      +/-   ##
==========================================
- Coverage   80.80%   80.78%   -0.03%     
==========================================
  Files         248      248              
  Lines       10859    10859              
==========================================
- Hits         8775     8772       -3     
- Misses       2084     2087       +3     

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