AVPlayer treats a progressive HTTP stream as a seekable, finite asset only when
the server honors Range requests. /file always returned 200 with the whole body
and no Accept-Ranges, so AVPlayer never resolved a duration and reported
end-of-track as AVPlayerItem.status == .failed ("Operation Stopped") instead of
AVPlayerItemDidPlayToEndTime. Because the .failed path never calls
onTrackFinished, the queue stalled and the next track never played.
Honor single-range requests (bytes=N-M, bytes=N-, suffix bytes=-N) with 206 +
Content-Range, advertise Accept-Ranges: bytes on every response, and return 416
for out-of-range; partial reads stream only the requested slice via FileHandle.
Add an end-to-end test that plays a track to its natural end through the real
provider + server and asserts a clean finish (no "Operation Stopped").
