Returns: Dict with success status and updated metadata:
success: Boolean indicating if the operation succeededbatch_id: The batch identifiermetadata: Complete metadata dictionary after merge
ValidationError: If metadata format is invalid (e.g., nested objects, non-string keys, invalid value types)NomadicMLError: If batch is not found or you don’t have permission to modify it
Only the batch owner can add or update metadata. New metadata keys will be merged with existing metadata, with new values overwriting any existing keys with the same name.Metadata values must be strings or integers only - nested objects, arrays, booleans, or null values are not supported.