Add GeoJSON vector data support, STAC layer support, and comprehensive tests

[giswqs]

Summary

This PR adds GeoJSON vector data loading support (issue #4), STAC raster layer support (issue #3), and rewrites the test suite from scratch.

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GeoJSON Support (closes #4 — partial: GeoJSON for MapLibre)

Added add_geojson() method to the MapLibre Map class with the following features:

Input formats supported:

• GeoJSON dictionary (FeatureCollection, Feature, or bare Geometry)
• Local file path (.geojson, .json)
• URL string (fetched client-side via JS fetch())
• Any object with __geo_interface__ (e.g., GeoPandas GeoDataFrame)

Capabilities:

• Auto-detects geometry types (Point, LineString, Polygon, Multi* variants) and creates the appropriate MapLibre layer type (circle, line, fill)
• For mixed-geometry FeatureCollections, creates multiple filtered layers automatically
• Computes bounding box and auto-fits the map (opt-out via fit_bounds=False)
• Supports custom paint, layout, source_options (e.g., clustering), before_id
• Sensible default styling for each layer type

Example usage:

from mapwidget.maplibre import Map

m = Map(center=[-77.03, 38.90], zoom=10)

# From a dict
m.add_geojson({"type": "FeatureCollection", "features": [...]})

# From a URL
m.add_geojson("https://d2ad6b4ur7yvpq.cloudfront.net/naturalearth-3.3.0/ne_110m_admin_0_countries.geojson")

# From a file
m.add_geojson("data/parcels.geojson")

# From a GeoDataFrame
import geopandas as gpd
gdf = gpd.read_file("data/roads.shp")
m.add_geojson(gdf, paint={"line-color": "red", "line-width": 2})

Note: This addresses the GeoJSON portion of #4 for the MapLibre backend. Shapefile support works indirectly via GeoDataFrame. Full Shapefile/GeoDataFrame direct loading for other backends (Cesium, Mapbox) is left for future work.

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STAC Layer Support (addresses #3)

Added add_stac_layer() method that:

• Fetches a STAC Item JSON from a URL
• Extracts the specified asset key's COG href (defaults to "visual")
• Loads it as a raster layer using the existing maplibre-cog-protocol
• Auto-fits the map to the STAC item's bounding box

Example usage:

m.add_stac_layer(
    "https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-2-l2a/items/...",
    asset_key="visual",
    layer_options={"paint": {"raster-opacity": 0.8}},
)

COG support was already implemented in add_cog_layer(). This builds on top of it for the STAC use case referenced in #3.

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Test Suite

Rewrote tests/test_mapwidget.py from a single placeholder test to 33 comprehensive tests covering:

• TestMapLibreMap — initialization, add_call, navigation methods, source/layer/control management
• TestAddGeoJSON — dict, file, URL, custom IDs, custom paint, error handling (TypeError, FileNotFoundError)
• TestComputeBounds — points, polygons, FeatureCollections, empty data, URL passthrough
• TestGetGeometryTypes — single type, mixed types, URL passthrough
• TestAddCogLayer — default and custom IDs
• TestAddStacLayer — default and custom IDs

All 33 tests pass.

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Files Changed

• mapwidget/maplibre.py — Added add_geojson(), add_stac_layer(), and helper methods
• mapwidget/js/maplibre.js — Added addGeoJSONToMap(), addStacLayer(), computeGeoJSONBounds() JS handlers
• tests/test_mapwidget.py — Complete rewrite with 33 tests

Refs: #3, #4

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