Streamline PreparationBloc & PreparationTaskHandler

**Is your feature request related to a problem? Please describe.**
A lot of code duplication is happening in the `PreparationBloc` & `PreparationTaskHandler`. It would be cool to deduplicate it.

**Describe the solution you'd like**
Code deduplication, maybe a "master" that can perform everything and only needs to be provided with small arguments or similar.

**Describe alternatives you've considered**
- Let it be

**Additional context**
More of a developer UX feature

Start by comparing the responsibilities and duplicated code in PreparationBloc and PreparationTaskHandler. Define the shared behavior and arguments before choosing an abstraction; done means the repeated logic is consolidated without changing existing preparation behavior.

Written by the indexing model from the issue text.