tests(#2406): add test_foliumap.py

[bruno-portfolio]

Summary

Adds unit test coverage for the foliumap module as requested in #2406.

Changes

Tests	Count
Map initialization	7
set_center	1
zoom_to_bounds	1
add_tile_layer	2
add_wms_layer	1
add_marker	3
add_geojson	4
add_heatmap	2
to_html	3
add_layer_control	1
set_control_visibility	1
setOptions	2
add_cog_mosaic	1
Total	29

Notes

• Module-level basemaps initialization requires import-time mocking (the from .common import * in foliumap.py shadows the basemaps module with a Box object)
• Uses tempfile.TemporaryDirectory() with with blocks per test
• All assertions verify actual state changes
• No alias tests