feat: departureId in PublicTransitEvent and in eqasim_pt.csv

[tkchouaki]

This PR adds a departureId attribute in the PublicTransitEvent objects to track the departure used during the simulation (the departure is determined during mobsim and not as part of the transit route). This allows to have a departureId column in the generated eqasim_pt.csv files.

Note
Since the departure ID information is not part of the route, it is not stored in the population file, so running the analyses from a plans file without and events file will generate an empty departure_id column.