Support for storing historical runs

Need to be able to manually specify creation, start and end times. To begin with:

• Run.init() needs additional options created, started and endtime (or similar). If not set, the server will set them (as it does now).
• Run.close() needs an additional timestamp option for specifying the end time. If not set, the server will set it (as it does now).

This doesn't take into account people using the context manager.

When creating a run the JSON body in the POST can include created and started. If there are no metrics then it can also include endtime and status set to completed. When updating the status of the run to completed the JSON body can include endtime.

Inizia tracciando Run.init() e Run.close(), quindi esamina come vengono assemblati i loro corpi JSON per creare e completare le run. Tieni conto del percorso del context manager e verifica che i timestamp storici opzionali preservino i valori predefiniti correnti del server, mentre le run completate inviino lo stato e l’ora di fine richiesti.