feat: expose all readModels sections

[michaelhallquist]

Summary

• generate private fields and active bindings for every readModels section inside the R6 class so each model instance maintains its own values
• load and clear all output sections dynamically via populate_output
• test that model exposes additional sections such as output and errors

Testing

• R -q -e "devtools::test()" (fails: command not found)
• apt-get update (fails: 403 Forbidden)

---

https://chatgpt.com/codex/tasks/task_e_68acb22931188321b2896941b5e1322c