- Add save_state/restore_state methods to CameraStage
- Add save_state/restore_state methods to DisplayStage
- Extend Pipeline._copy_stage_state() to preserve camera/display state
- Add save_state/restore_state methods to UIPanel for UI state preservation
- Update pipeline_runner to preserve UI state across preset changes
Camera state preserved:
- Position (x, y)
- Mode (feed, scroll, horizontal, etc.)
- Speed, zoom, canvas dimensions
- Internal timing state
Display state preserved:
- Initialization status
- Dimensions
- Reuse flag for display reinitialization
UI Panel state preserved:
- Stage enabled/disabled status
- Parameter values
- Selected stage and focused parameter
- Scroll position
This enables manual/event-driven rebuilds when inlet-outlet connections change,
while preserving all relevant state across pipeline mutations.