Generate and persist UMA model IDs

[lbluque]

Summary

• generate random IDs for untagged UMA MoE models
• broadcast generated IDs from rank zero across distributed workers
• persist resolved IDs in resume, DCP, and inference checkpoint configs
• add IDs to UMA benchmark configs
• add coverage for generation, broadcasting, and checkpoint persistence

Testing

• 33 focused unit tests passed
• DCP train/save/load integration test passed
• pre-commit passed