editoast: stdcm: pre-filter train requirements that can't affect the new train

[eckter]

When editoast build the stdcm request to be sent to core, it fetches all the train requirements for the scheduled trains. See here

At this point, we know when the train is supposed to start and when it will end (based on max running time). We could easily pre-filter the train requirements to only include the ones in this window.

It would make the request smaller (they're currently around 20MB for an imported timetable), and it would speed some things up in core. We could do the filtering on the core side, but we'd miss out on the request size reduction.

It's a prerequisite for stdcm requests in timetables that span over more than a few hours.