Add automated structure impact assessment to flood pipeline

[cmspeed]

This PR introduces a new automated impact analysis step to the flood pipeline to estimate the number of flooded structures within an Area of Interest (AOI). It evaluates the cumulative maximum flood extent (MAX-EXTENT) against OpenStreetMap (OSM) building footprints using geometric intersection.

Note: To run the impact analysis step the disasters environment must be rebuilt using the updated environment.yml attached to this PR.

Updates

• A new file,impact.py, adds functions for estimating the impact to OSM structures. This is integrated into run_max_extent_pipeline. The structure impact analysis runs automatically in the background immediately after the maximum flood extent raster is successfully generated.

• To conserve memory and prevent OSM API timeouts, the script divides the raster into 15x15km (500x500 pixel) windows. It queries the OSM Overpass API for building footprints in chunks that actively contain flooded pixels.

• The spatial logic guarantees accuracy for buildings smaller than a 30m pixel. It uses all_touched=True to capture any water touching a structure, vectorizes those pixels into Shapely polygons, and calculates the fractional overlap. A building is flagged as impacted if at least 50% of its exact footprint is covered by water.

• The pipeline automatically outputs two new datasets: a .geojson file containing the impacted building footprints and a .csv containing the impacted building centroids.

• Updates to environment.yml:
  - Added osmnx to support the new OpenStreetMap building footprint queries.