Fix TopoJson rendering for single-geometry objects

[adarshsm]

Closes #1816.

The bug

A TopoJSON object can be either a GeometryCollection (which has a geometries list) or a single geometry — Polygon, MultiPolygon, LineString, etc. — which has no geometries key and is itself the feature. TopoJson.style_data() assumed the former and did resolved_object["geometries"] unconditionally, so any single-geometry object crashed on render:

File ".../folium/features.py", line 981, in style_data
    geometries = recursive_get(self.data, self.object_path.split("."))["geometries"]
KeyError: 'geometries'

Minimal reproducer (from the issue, trimmed):

import folium

topo = {
    "type": "Topology",
    "transform": {"scale": [1, 1], "translate": [0, 0]},
    "objects": {"A": {"type": "Polygon", "id": "A", "arcs": [[0]]}},
    "arcs": [[[0, 0], [0, 10], [10, 10], [10, 0], [0, 0]]],
}
folium.TopoJson(topo, "objects.A").add_to(folium.Map())  # KeyError: 'geometries' on render

The fix

Branch on the object's type: iterate geometries for a GeometryCollection (unchanged), otherwise treat the object itself as the single feature to style. The JS side (topojson.feature) already handles both shapes, so only the Python styling pass needed the guard.

Tests

Added test_topo_json_single_geometry, which renders a single-Polygon TopoJSON and asserts the style_function is applied to the geometry. It fails with KeyError on main and passes with this change; the existing GeometryCollection path is unchanged and still covered.

[adarshsm]

Closing this — I hadn't spotted that #2250 already addresses this issue (and covers a second crash site in the popup/tooltip path that this PR misses). #2250 is the more complete fix; deferring to it. Apologies for the noise.

[KhadeerBasha1232]

Thanks for deferring to this one, @adarshsm — and thanks again for catching the second crash site in the Popup/Tooltip path during review, that made the fix in #2250 much more complete. Appreciate all the help!