Client: Fix orphaned Python process leading to plotting issues

Follows on from https://github.com/ISISComputingGroup/IBEX/issues/7674.

As described in the previous ticket, change the client so that it calls the Windows API to be put into a job object with the `JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE` flag. This should be done as early as possible in client startup so it will terminate any process spawned by the client, not just python spawned by pydev, no matter how IBEX closes.

## Reproducible?
Yes

### To Reproduce (orphaned process)
- Run `sleep` in Scripting.
- End the client process from task manager.

### To Reproduce (plotting issues)
- Plot something in a Scripting console.
- Plot something in another Scripting console.

### To Reproduce (plotting issues, alternate way using the orphaned process)
- Plot something in a Scripting console.
- Run `sleep`.
- End the client process from task manager.
- Plot something in a Scripting console again.

## Acceptance criteria
- [ ] Issue is fixed.