MvtSpriteAtlasLoader

Fetches a Mapbox sprite atlas (<stem>.json manifest + <stem>.png packed image) from a URL stem and returns a populated MvtSpriteAtlas. The two fetches run sequentially — sprite endpoints typically serve both responses from the same edge node so concurrency doesn't save much round-trip time.

For HiDPI displays, the standard Mapbox convention is <stem>@2x.json / <stem>@2x.png; pass stem with the @2x suffix already appended if you want the higher-resolution variant.