fix(vite): use '' key for root scope in variable collector

[ah-dc]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

The key of the root scope should be an empty string instead of '0'. I didn't notice this mistake because all setup script code will be put in a nested scope, so I introduced a test case to verify if it can correctly analyze the normal code.

Besides this, I think these code need to be refactored and have independent tests, but currently I don't have good ideas of that.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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