feat(tasks): one-time tasks

[schplitt]

🔗 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)
• [x] ✨ 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

📝 Checklist

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

Implements scheduled one time tasks for #1974

Croner only ever runs on full seconds, so the actual wait time may be slightly after the specified time.
I added a test that runs a scheduled task. Sadly, I didn't find a way to use Vitest's mock timers to artificially advance the Cron job.