Filters in cold cases justice screen are not working

[agnieszka-dev]

DFHack 52.04-r1

[Alistair-Afton]

Found it. The justice filters never applied on the Cold cases tab because the unit list lookup preferred the hidden "Open cases" widget. Named widget lookup finds hidden tabs, so the filter was always installed on (and refreshes sent to) the open cases list even while cold cases was visible.

Fixed in #5927 by selecting the currently visible tab instead. Added tests covering both tabs for the interrogate and convict lists.