XetSession download test

Build the WASM package first: ./build_wasm.sh, then serve this directory with a static server (e.g. python3 -m http.server 8080) and open http://localhost:8080/examples/download.html.

The page calls two Hugging Face Hub endpoints to derive the inputs needed by XetDownloadStreamGroup.downloadStream(...):

  1. POST /api/{repo_type}s/{namespace}/{repo}/paths-info/{revision} — returns xetHash and size for the file
  2. GET /api/{repo_type}s/{namespace}/{repo}/xet-{token_type}-token/{revision} — returns { accessToken, exp, casUrl }
Ready.