front: application is slow when opening a big timetable

[bloussou]

What happened?

Rolling stock images are sometimes not here:

moving the mouse over different part of the page is very slow...

What did you expect to happen?

Backend is pretty fast, is there a way to immprove the speed here ?

How can we reproduce it (as minimally and precisely as possible)?

Go here: https://rec-osrd.reseau.sncf.fr/operational-studies/projects/4/studies/198/scenarios/362 (1000 different trains timetable)

1. move your mouse over the list of trains
2. click on different trains
3. when clicking on a train check the map and tables

On which environments the bug occurs?

Recette (SNCF)

On which browser the bug occurs?

Firefox

OSRD version (top right corner Account button > Informations)

3eecd56

[bloussou]

Probably here : https://github.com/OpenRailAssociation/osrd/blob/dev/front/src/utils/date.ts#L88

dayjs.tz.guess(), // Format : 'Europe/Paris'

Same for conflict cards