Draft: Fix compliance of ActsTrk::MultiTrajectory with the test
Previously, we were not actually testing the compliance of ActsTrk::MultiTrajectory, instead we were just testing Acts::VectorMultiTrajectory.
This MR changes this, and tries to actually fix the compliance. I haven't run the full suite of tests so far.
This is dependent on some features of ACTS version 38.0.0, which we hope to tag and deploy at the end of the week.