AthSimulation CI tests rework
- remove obsolete
G4ExHive
(also from Athena) - add MT tests with 4 threads and using ComponentAccumulator for Run 2, 3 and 4 (including reference comparisons)
- split checks of MT tests to improve parallelisation
- also add legacy config tests for Run 2 and 3 that use the same reference
- add HITS merging with sorting (including reference comparison) based on the Run 3 test output
- add HITS filtering test with a fixed input (including reference comparison)
As Run 4 test now also has a reference adapt Athena Run 4 tests to disable references there.
Run time is comparable to before the rework.