feat: add NATS, etcd, and HF cache verification to sanity_check.py

- Add etcd service monitoring with key listing and cluster info
- Add NATS service monitoring with subject and subscription details
- Add Hugging Face cache inspection showing cached models
- Keep dynamo_check.py as symlink to sanity_check.py for compatibility
- Reorder checks: services, file system, HF cache, then dev tools

Signed-off-by: Keiven Chang <[email protected]>

Author: keivenchang