Fine-tune jobs and checkpoints return Together model registry IDs

Fine-tune job and checkpoint responses now include Together model registry IDs for completed artifacts. Use model_object_id and model_object_revision_id on completed jobs, adapter_object_id and adapter_object_revision_id on LoRA jobs, and object_id and object_revision_id on list checkpoints entries to reference weights in the model registry. The Together Python SDK (2.24+) and Together TypeScript SDK expose these fields on retrieve and list-checkpoints responses.