[pycue] Proc type uses wrong attribute for booked_time

**Describe the bug**

The api wrapper proc.py implements a function bookedTime that fails with AttributeError.

**To Reproduce**

```python
host = opencue.api.findHost("")
procs = host.getProcs()
proc = procs[0] # type(proc) == opencue.wrappers.proc.Proc
proc.bookedTime() # AttributeError: 'Proc' object has no attribute 'booked_time'
```

Start in the pycue API wrapper's proc.py and inspect the bookedTime function alongside the Proc attributes it uses. Verify the attribute name against the Proc object, then reproduce the example call to confirm bookedTime no longer raises AttributeError and returns the booked time.

Written by the indexing model from the issue text.