fix: transition `onComplete` triggers after each property animation

[BobbieGoede]

🔗 Linked issue

• 188

❓ 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

During work on #188 I ran into two issues which made it difficult to test variants using the transition onComplete function:

• onComplete is called after every variant property animation completion
• When the event variants feature is enabled, variant animations are triggered twice (instantly)

This PR expands on #188 by fixing those issues (so that PR description still applies), I created this separate PR because it touches on more than just the tests.

📝 Checklist

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

[rylanharper]

I don't think this ever got pushed to the latest version?