- remove UI-specific state (the enabled schedulers) from redux, instead derive it in a selector
- simplify logic by putting schedulers in an object instead of an array
- rename `activeSchedulers` to `enabledSchedulers`
- remove need for `useEffect()` when `enabledSchedulers` changes by adding a listener for the `enabledSchedulersChanged` action/event to `generationSlice`
- increase type safety by making `enabledSchedulers` an array of `SchedulerParam`, which is created by the zod schema for scheduler