Playtime: Save ignited  state of slots when Reaper project is closed.  (Feature Request)

### Discussed in https://github.com/helgoboss/helgobox/discussions/1048

<div type='discussions-op-text'>

<sup>Originally posted by **atencion** July 20, 2024</sup>
It would be great if the playback (or "ignited") state of slots is saved as part of the project. It used to be the case in Playtime 1, and would make sense to save it in Playtime 2 as well.  

Thank you! </div>