Decodes a PNG/WebP DEM tile (bytes) to an size × size Float32 height grid in meters.
Uses createImageBitmap + an OffscreenCanvas read-back, so it runs in the
browser (and workers); it is intentionally absent from the pure demToQuantizedMeshTile
path so that stays unit-testable without a canvas.
Decodes a PNG/WebP DEM tile (bytes) to an
size × sizeFloat32 height grid in meters. Uses createImageBitmap + an OffscreenCanvas read-back, so it runs in the browser (and workers); it is intentionally absent from the pure demToQuantizedMeshTile path so that stays unit-testable without a canvas.