Improve camera_apple robustness and lifecycle handling

- App pause/resume: Stop camera capture on background transition and
  restore on foreground, preventing resource leaks
- Row stride: Handle pixel buffer row stride != width to prevent
  data corruption on devices with padded buffers
- Device lock: Track lock state and properly unlock on deactivation
- Input/output validation: Check canAddInput/canAddOutput before
  adding to capture session, with proper cleanup on failure