merging trajectories can throw away trajectory timing

[v4hn]

When a stage merges trajectories (either Connect, doing it implicitly or a Merger stage), the trajectories time parameterization is computed from scratch with hard-coded scaling factors.

This can unexpectedly speed up trajectories that were explicitly slowed down.

From my perspective, a proper solution to this issue is to implement a merge algorithm that does not recreate the time parameterization, but resamples the parameterized trajectories into one single trajectory.