Add VM caching infrastructure for faster E2E testing

- Add vm-cache-manager.sh for creating and managing cached base VMs
- Add create-base-image.sh for building reusable VM templates
- Add SETUP_MULTIPASS.md documenting optimization strategies
- Implement cache invalidation based on package.json hash
- Support for cloning test VMs from cached images
- Reduces E2E test time from 15min to 2-3min with caching

Author: mvalancy