Existing Marker and Geometries disappear when adding or removing Calculations

**Browser: Firefox**

As the title states. When adding new via points, moving pins or adding new isochrones etc. already placed pins and geometries disappear for a second and are added together with new results.

Since we are always only dealing with one route at a time, I guess that is ok. But for Isochrones, it's a little confusing. Especially when the new calculation takes longer and they all disappear for quite some time.

I'm also discovering longer calculation times for Isochrones when I'm adding more. Are existing Isochrones always recalculated?
**Isochrones Example**

[Isochrones Example](https://github.com/user-attachments/assets/013a1537-29cf-472c-a22e-857cf78b503b)

**Routes Example**

[Routes Example](https://github.com/user-attachments/assets/3c7a485e-8578-46de-9062-ee5c1812dc9e)

Reproduce the issue in Firefox using the linked Isochrones and Routes examples while adding or removing calculations. Trace the map update and calculation flow to determine why existing markers and geometries disappear, then verify that they remain visible during new calculations and that existing isochrones are not unnecessarily recalculated.

Written by the indexing model from the issue text.