Unify USB update node_config backup flow

[BxNxM]

Summary

• use _backup_node_config to fetch node_config for version comparison and carry devfid metadata through USB updates
• allow deploy_micros to accept a provided node_config bundle to avoid redundant downloads while restoring backups
• return serialized node_config from backup operations so subsequent steps reuse the same data

Testing

• python -m compileall toolkit

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Codex Task