metadata API: serialization is missing a final newline

Our JSON serialization is basically json.dumps(metadata_obj.to_dict(), ...).encode("utf-8")

json.dumps() return value does not end in a newline. This means any files written with this content will not end in a newline: this makes the produced files not valid posix text files.

For Metadata.to_file() this seems like a minor bug (and Metadata.to_bytes() should have the same output for consistency), so in practice JSONSerializer.serialize() probably should add the final newline.

My only concern about this is that it is an unexpected change in the serialization output... IF we change this, we should definitely consider this an API change for users who produce metadata.

Inizia da JSONSerializer.serialize(), quindi esamina Metadata.to_file() e Metadata.to_bytes() per confrontare il loro output attuale. Conferma il comportamento previsto per la nuova riga finale e valuta l’impatto sulla compatibilità dell’API di serializzazione prima di decidere quali test o documentazione debbano essere modificati.