support single scan iteration on musst, jog motor, calc acq devices
For some scans like fscanloop / pcotomo, we need to have support for single scan iteration on musst, jog motor, calc devices. In those scans, some devices will iterate while others musst be prepared/started only once. Update needed:
- on musst acquisition master : implement prepare_once / start_once
- on jog motor master : implement start_once
- on calc slave devices : inherit prepare_once / start_once from master device if possible
In addition to that, a few add-ons are needed:
- on jog motor master : implement undershoot_start_margin as on other motor master
- on lima master : add an event when the lima device has been started. Used in scans to know when lima device is ready to receive new triggers.