🧪 Add tests for normalizeModelKey

[akutuva21]

🎯 What: The testing gap for the normalizeModelKey utility function in scripts/validate-metadata.js was addressed. The function is now explicitly exported and tested.
📊 Coverage: The new test suite covers the following scenarios:

• Case-insensitive removal of .bngl extensions
• Stripping of non-alphanumeric characters
• Conversion of input to lowercase
• Edge cases including empty strings, null, and undefined
  ✨ Result: Test coverage for validate-metadata.js is improved, ensuring the model key normalization logic is robust and preventing future regressions.

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PR created automatically by Jules for task 18159973778207655746 started by @akutuva21

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