Add preliminary NSW digi and overlay ART tests
Add preliminary NSW digi and overlay ART tests:
- standard digi with MC16a-like pile-up
- presampling for MT with MC16a-like pile-up
- presampling for legacy overlay with MC16a-like pile-up
- legacy and MT-ready overlay comparison (serial)
Also fixing a comparison for an equivalent MC16 legacy vs MT-ready overlay test.
Regression tests between nightlies are currently disabled as I suspect things will still change often.