Merge branch 'fix/unused-variables' into 'master'

Fix/Unused Variables

Going through some of the warnings my IDE is throwing up so I'll probably end up doing a couple of these tiny pull requests.

- `cal_tools/cal_tools/agipdlib.py`: `corr_bools={}` setting keyword arguments to mutables isn't a great idea since the state can persist across function calls, maybe in this case that was the intention but it usually isn't. Changed it to `None` and then set it to a dict if no argument is given.
- `cal_tools/cal_tools/lpdlib.py`: `self.cnl = True` was set, but it looks like that should have taken its value from the `correct_non_linear` argument, set it to that.
- `cal_tools/cal_tools/metrology.py` an `offset` is defined but never applied to the coordinates. Similar code appears throughout the file so I just did the same thing there as well, think it should be correct.

See merge request detectors/pycalibration!415