reloadBaseMapTiles

Drop the base map's in-memory tile cache and force a re-read from the MBTiles file on disk. Use this after the engine merges new tile data into coreEngineFiles/map.mbtiles (per-property or world basemap downloads). Without this, the MBTilesTileDataSource keeps serving stale tiles cached at first read — the user sees a "missing square" of streets/roads until they zoom out and back in (the zoom change happens to fetch tile coordinates not in the cache).

Lightweight: just drops the in-memory tile cache. Does NOT recreate the data source, decoder, or layer (a full loadBaseLayer rebuild was tried in commit 88efc59 and caused ANRs when multiple property downloads completed back-to-back).