Add support for subprocesses

I'm trying to generate nodes from a JSON list. There are 2 limitations that subprocess solves:

1. using only custom events triggers a 2 loop limit on recursive cycles. there's no way (in settings) to bump this limit without touching code...hoping not to touch code. Would be great if we could add this to settings or the model configuration
2. I was able to solve it using Queues but that requires running cron (so it's not immediate)

Subprocesses seems to resolve both of these issues if they were available.

To convert an action to a subprocess:
1. add an action to the model board
2. save the model
3. click on the action to see the "wrench" icon...see attachment Screenshot 2026-02-22 at 10.42.50 AM.png (this isn't visible without the Save action)
4. clicking on wrench gives you subprocess options...see attachment Screenshot 2026-02-22 at 10.42.56 AM.png