i15-1: Work out how the cryostream works with the cobra

The cryostream and the cobra share the same PV for their motor. Presumably this is because they are mounted on the same rail on the table. However they have different `safe_position` values in `xpdfLocalParameters.xml`:
```
"cobra": {
"safe_position": "2.0",
"beam_position": "461.5",
},
"cryostream": {
"beam_position": "469.9",
"safe_position": "0",
}
```

Also, the robot load code in scripts only puts the cobra and blower into a safe position, not the cryostream (although if they share a PV this would move the cyrostream if it were mounted instead of the cobra?). The only time the cryostream is moved to safe other than in visit scripts, is here in `generic_scanrequests.py`, which suggests that the cryostream is moved to safe after each scan unless `return_to_temperature` is not None.
```
if return_to_temperature is not None:
if str(return_to_temperature).lower() == "off":
after_scan["cryostream.setTemperature"] = 300
after_scan["cryostream.move_to_safe"] = None
```

We should investigate how this works and update the devices and robot load plan accordingly.

## Acceptance Criteria
- The above is investigated
- The correct behaviour is added into the dodal devices and robot load plan

Start by tracing the shared motor PV and the differing safe_position values in xpdfLocalParameters.xml, then inspect the robot load code in scripts and the cryostream handling in generic_scanrequests.py. Confirm the expected cryostream and cobra behavior, update the dodal devices and robot load plan accordingly, and verify that the acceptance criteria are met.

Written by the indexing model from the issue text.