Features/costs calculation

[birgits]

Description

Adds a new function that calculates grid expansion costs from a diff of the original grid and the reinforced grid. The reason this is needed is, that costs are currently calculated using Results.equipment_changes. However, this is prone to bugs when equipment changes aren't tracked correctly.
The following needs to be done:

• Add and test new costs function
• Store original grid in Topology.original_grid_topology when it is loaded from ding0 - needs to be stored to and restored from csv as well
• Add function to overwrite original grid topology

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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