Avoid leakage of flows data between subsequent runs

[FlxPo]

Running multiple seeds (sequentially or in parallel) could contaminate congestion because OD flows and congested artifacts were written to shared fixed paths (e.g. path_graph_car/simplified/flows.parquet, travel_costs_congested_car.parquet). This produced bimodal / unstable results and made parallel runs unsafe.

Changes

• Added a first-class flows asset:

  • mobility/transport_costs/od_flows_asset.py (VehicleODFlowsAsset)
  • Persists only from,to,vehicle_volume (minimal input needed for congestion).
  • Keyed by PopulationTrips.inputs_hash (includes seed) + iteration + mode_name.
  • Always writes a parquet with the expected schema (can be empty).

• Added congestion “variant/snapshot” assets (per run/iteration):

  • mobility/transport_graphs/congested_path_graph_snapshot.py
  • mobility/transport_graphs/contracted_path_graph_snapshot.py
  • mobility/transport_costs/path_travel_costs_snapshot.py
    These depend on stable base artifacts + VehicleODFlowsAsset, producing isolated congested graphs/costs safe for parallel runs.

• Rewired update propagation in the iterative loop:

  • mobility/choice_models/population_trips.py passes run_key=PopulationTrips.inputs_hash into cost updates.
  • mobility/choice_models/state_updater.py calls TravelCostsAggregator.update(..., run_key, iteration).
  • mobility/choice_models/travel_costs_aggregator.py builds VehicleODFlowsAsset and passes it to PathTravelCosts.update.

• Made PathTravelCosts prefer the current snapshot for get(congestion=True):

  • mobility/transport_costs/path_travel_costs.py stores a pointer to the latest snapshot.
  • If no snapshot was applied, congestion=True falls back to free-flow to avoid reusing stale shared congested caches.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.42%. Comparing base (c8c3ac3) to head (680565d).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #260   +/-   ##
=======================================
  Coverage   70.42%   70.42%           
=======================================
  Files          56       56           
  Lines        2424     2424           
=======================================
  Hits         1707     1707           
  Misses        717      717           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.