Allow custom Series/dict for line_color and node_color in plot_plotly (issue #385)

[nader-00]

This PR extends edisgo.tools.plots.plot_plotly to support custom colors for lines and nodes.

What changed

• line_color now accepts, in addition to existing string options, a pandas.Series or dict
  mapping branch_name → color (e.g. "red", "#ff0000").
• node_color now accepts, in addition to existing string options, a pandas.Series or dict
  mapping bus_name → color.
• For custom colors:
  • Colors are taken directly from the provided Series/dict.
  • Lines/nodes that are not present in the Series/dict fall back to a default grey color.
  • No colorbar is shown (only explicit colors are used).
• Existing behaviour for string options ("loading", "relative_loading", "reinforce",
  "voltage_deviation", "adjacencies") is unchanged.

Usage examples

import pandas as pd
from edisgo.tools import plots

# Example: color two specific lines
line_colors = pd.Series({
    "line_1": "red",
    "line_2": "orange",
})

# Example: color some buses
node_colors = {
    "bus_1": "blue",
    "bus_5": "purple",
}

fig = plots.plot_plotly(
    edisgo_obj,
    line_color=line_colors,
    node_color=node_colors,
    plot_map=False,
)