Add Nominatim API for load_overture_data by a parameter place_name

[yu-ta-sato]

Description

This pull request introduces the Nominatim API to support place-based queries, add topological clipping for network data, and provide new utilities for removing isolations.

Boundary and area handling improvements:

• Added the get_boundaries function to retrieve polygon boundaries for named places using Nominatim geocoding, enabling place-based queries in load_overture_data.
• Updated load_overture_data and _prepare_area_and_bbox to accept and process a wider range of area types, including bounding boxes, polygons, multipolygons, GeoSeries, and GeoDataFrames, with automatic CRS handling and mutual exclusion with place name. [1] [2] [3] [4]

Graph processing and clipping utilities:

• Introduced the clip_graph function in utils.py for topological clipping of network graphs, preserving network integrity when clipping segments, and integrated it into _download_and_process_type for segment data. [1] [2]
• Added remove_isolated_components to filter graphs to their largest connected component, improving downstream graph analysis. [1] [2]

Robustness and usability enhancements:

• Improved handling of GeoJSON output from subprocesses in _download_and_process_type, including parsing stdout and filtering for valid geometries and exploding MultiLineStrings. [1] [2]
• Added warnings in process_overture_segments for missing or geographic CRS, guiding users toward best practices for spatial analysis.

These changes collectively make the package more flexible, robust, and user-friendly for spatial data analysis and network graph operations.

Related Issues

#114

Checklist

• I have read the Contributing Guide.
• I have updated the documentation, if necessary.
• I have added tests to cover my changes.
• All new and existing tests passed.
• Pre-commit checks passed locally.

[codecov]

Codecov Report

❌ Patch coverage is 92.52336% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
city2graph/utils.py	85.10%	7 Missing ⚠️
city2graph/data.py	98.33%	1 Missing ⚠️

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