Feat/road_congestion

[alexandermorozzov]

An update to the network analysis workflow in feat/road_congestion:

• Reworked origin_destination_matrix to use an origin-constrained gravity model with integer OD output.
• Added robust integerization (largest-remainder rounding) so each origin row sum is preserved exactly.
• Added fallback for isolated origins by assigning demand to intrazonal flows.
• Renamed services_dfs to services_count_dfs for clearer semantics.
• Refactored road_congestion to a capacity-aware MultiDiGraph assignment:
  • lane normalization from mixed input formats,
  • per-edge capacity and intensity,
  • trip-by-trip shortest-path loading,
  • dynamic removal of oversaturated routing edges,
  • final congestion_level = intensity / capacity.
• Added full docstrings for both public functions (origin_destination_matrix, road_congestion).
• Updated examples/analysis/network/od_and_rc.ipynb.