fix: cancel volume server requests on client disconnect during S3 downloads (#8373)

* fix: cancel volume server requests on client disconnect during S3 downloads

- Use http.NewRequestWithContext in ReadUrlAsStream so in-flight volume
  server requests are properly aborted when the client disconnects and
  the request context is canceled
- Distinguish context-canceled errors (client disconnect, expected) from
  real server errors in streamFromVolumeServers; log at V(3) instead of
  ERROR to reduce noise from client-side disconnects (e.g. Nginx upstream
  timeout, browser cancel, curl --max-time)

Fixes: streamFromVolumeServers: streamFn failed...context canceled"

* fixup: separate Canceled/DeadlineExceeded log severity in streamFromVolumeServers

- context.Canceled → V(3) Infof "client disconnected" (expected, no noise)
- context.DeadlineExceeded → Warningf "server-side deadline exceeded" (unexpected, needs attention)
- all other errors → Errorf (unchanged)"

weed/util/http/http_global_client_util.go

@@ -311,11 +311,11 @@ func ReadUrlAsStream(ctx context.Context, fileUrl, jwt string, cipherKey []byte,
 		return readEncryptedUrl(ctx, fileUrl, jwt, cipherKey, isContentGzipped, isFullChunk, offset, size, fn)
 	}
 
-	req, err := http.NewRequest(http.MethodGet, fileUrl, nil)
-	maybeAddAuth(req, jwt)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, fileUrl, nil)
 	if err != nil {
 		return false, err
 	}
+	maybeAddAuth(req, jwt)
 
 	if isFullChunk {
 		req.Header.Add("Accept-Encoding", "gzip")