fix(nuxt): ensure we only increment hydrating count once

[danielroe]

🔗 Linked issue

resolves #22022

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 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

In some cases, vue router can end up re-executing the render cycle of a component more than once in hydration. In this case, we can avoid incrementing the hydration counter by moving it out of the render function and into setup, which is also a performance improvement.

📝 Checklist

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

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