feat(plot): add voltage-over-distance comparison plots for LV and MV

[nader-00]

Description

This PR adds Plotly-based “voltage over distance” comparison plots to eDisGo.

It introduces two new methods on EDisGo:

• plot_voltage_over_dist(mv_id, lv_id, other, save_as=False, split_branches=False)
  LV voltage (p.u.) vs. shortest-path distance to the MV/LV transformer; compares two EDisGo objects and visualizes load/feed-in worst cases. Includes LV tolerance band (0.90–1.10 p.u.).

• plot_voltage_over_dist_mv(mv_id, other, save_as=False)
  MV voltage (p.u.) vs. shortest-path distance to the HV/MV transformer; compares two EDisGo objects and visualizes load/feed-in worst cases. Includes MV tolerance band (0.96–1.06 p.u.).

Distances are computed using Dijkstra shortest paths on the grid graph. Export to HTML/PNG is supported via save_as. Core logic is implemented in edisgo/tools/voltage_over_distance.py with thin wrappers in edisgo/edisgo.py. Tests are added (skipped when results.v_res is empty in the default fixture).

Fixes #565

Type of change

• New feature (non-breaking change which adds functionality)

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/env files
• I have added new features to the corresponding whatsnew file