fix: prevent preset variants from being mutated

[BobbieGoede]

🔗 Linked issue

• 74

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation, readme or JSDoc annotations)
• [x] 🐞 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

Resolves #74

This changes the way directive presets are handled, the underlying issue is similar to the one solved in https://github.com/vueuse/motion/pull/173, the preset variants are passed and reused and mutated down the line which is most noticeable in situations such as https://github.com/vueuse/motion/issues/74#issuecomment-1721145546.

To prevent this fix from influencing users variants (I suppose there are use cases where mutating a single motion is desired) I tried to only apply this change to directive presets.

📝 Checklist

• [x] I have linked an issue or discussion.
• [ ] I have added tests (if possible).
• [ ] I have updated the documentation accordingly.