Convert between state- and event-based data representations

[Peter9192]

• PEP725 is event-based (when did the leaves turn green?)
• NPN is state-based (where the leaves green on any given day?)
• PPO tried to harmonize both into a state-based dataset

In springtime, we now use event-based representations. However, for certain ML algorithms, state-based representations might make more sense. It would be great if we could find a way to easily transform between a state-based and an event-based data representation.