- Add plugin_loader.rs with FileBoxProxy implementation
- Integrate dynamic FileBox into interpreter (execute_new, method calls)
- Add feature flag 'dynamic-file' support throughout
- Create test program test_dynamic_filebox.nyash
- Plugin builds in 2.86s (vs main build 2+ minutes\!)
Build time improvement confirmed:
- Plugin-only build: 2.86s ✨
- Main build: 2+ minutes (timeout)
Next: Complete testing once main build finishes
