Reshape layoutlib fallback into Paparazzi runtime layout

[jwoglom]

Summary

• expand the Maven-provided layoutlib dependency into a synthetic runtime directory under build/composePreviews/layoutlib/<version> so Paparazzi sees the expected data/layoutlib.jar layout
• cache the extracted runtime with a SHA-256 marker and eagerly unpack any bundled data/ payloads while guarding concurrent extraction with a shared lock
• document the partial completion in the compose screenshot implementation plan

Testing

• not run (not requested)

---

https://chatgpt.com/codex/tasks/task_e_68d7f96469e4832cbd7ba048f1e37ab3