Improve the way boundaries are plotted in plot_basemap

[roeldegoede]

Kind of request

Changing existing functionality

Enhancement Description

We now first vectorize the msk=2 or msk=3 cells into a line, before we plot the boundaries in the plot basemap. This doesn't work for unstructred grids (future work), and seems a bit too complex in general for very simple functionality.

• We could convert the msk=2 cells to "dots", so no conversion to linestrings is needed
• We could consider plotting the raster/unstructred mask, but only the boundary cells, replacing the normal active domain (msk=1) with nans.

Use case

No response

Additional Context

No response