Update MIGRATION_PLAN.md with ONLYDUST and phase 2

[Villarley]

Add section for ONLYDUST and phase 2 of migration plan.

Pull Request Overview

Closes #201

📝 Summary

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Related Issues

• Closes #(issue number) Replace with actual issue number.

Type of Change

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• 📝 Documentation (updates to README, docs, or comments)
• 🐛 Bug fix (non-breaking change which fixes an issue)
• 👌 Enhancement (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)

🔄 Changes Made

What's Changed

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Implementation Details

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Technical Notes

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🔧 Tests Results

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Test Coverage

• Unit Tests
• Integration Tests
• Manual Testing

Evidence

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Testing Notes

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🔜 Next Steps

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