Add Google Generative AI Dart to Machine Learning section

[Ahmedatef5O5]

Add Google Generative AI Dart to Machine Learning section

This PR adds the official Dart/Flutter SDK for Google AI (Gemini) to the Machine Learning section.

The package provides:

• Text generation (LLMs)
• Multimodal input/output
• Embeddings API
• Image understanding & vision tasks
• Fully supported by Google and regularly updated

Repository: https://github.com/google-gemini/generative-ai-dart

This addition enhances the Machine Learning category with a modern, actively maintained AI package that enables advanced AI capabilities directly in Flutter and Dart applications.

Please read How to contribute before creating a submission.

Description and links to repo and pubdev if any

Submission description/links here

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Checklist

• [x] I read How to contribute
• [x] I edited the SOURCE.md file only
• [x] Added a link to the repo in the PR

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