Return XRC locations in physical coordinates rather than boxes

From a hyperion point of view it will be a lot cleaner if zocalo returned results in mm/um rather than boxes so that we do not have to do the conversion in the DAQ side. The setpoints of the gridscan should already be written to the nexus file and are already read by the 3D XRC anyway (https://github.com/DiamondLightSource/python-dlstbx/blob/75915e38e138fe0c90d4ab1dd1a9ec2b76f6afb3/src/dlstbx/cli/gridscan3d.py#L95). Additionally, the readback values of the gridscan will soon be in there too https://github.com/DiamondLightSource/mx-bluesky/issues/597.

## Notes
* This may require some correction on the hyperion side if we're not correctly writing the positions, see https://github.com/DiamondLightSource/mx-bluesky/issues/414
* We will probably want to keep the box co-ordinates in the result too as they may be useful

## Acceptance
* Zocalo additionally returns XRC results in position coordinates