refactor: migrate to Leaflet V2

Once @Maxel01 [vue-leaflet](https://github.com/Maxel01/vue-leaflet) is ready, we should migrate and go all-in on [Leaflet V2](https://leafletjs.com/2025/05/18/leaflet-2.0.0-alpha.html). This includes : - Making sure existing components still work - If there are breaking changes, elegantly document them - Documenting new components or composables - Making sure Leaflet Plugins are still usable in some way ?