Fix MV grid topology marker size for small grids

[jldonner]

Description

Fixed the way eDisGo/edisgo/tools/plots.py/plot_mv_grid_topology() > mv_grid_topology() > nodes_by_technology() calculates / depicts the size of buses by norming the size_dict that is responsible for this method by using the grid area. Grid area is now a new parameter in nodes_by_technology().

Fixes #700

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• New and adjusted code is formatted using the pre-commit hooks
• New and adjusted code includes type hinting now
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The Read the Docs documentation is compiling correctly
• If new packages are needed, I added them the setup.py, and if needed the rtd_requirements.txt, the eDisGo_env.yml and the eDisGo_env_dev.yml.
• I have added new features to the corresponding whatsnew file

grid 30879 (big, 1963 nodes)

grid 32377 (small, 396 nodes)