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/s3api/s3api_object_handlers.go

@@ -1093,7 +1093,16 @@ func (s3a *S3ApiServer) streamFromVolumeServers(w http.ResponseWriter, r *http.R
 		BucketTrafficSent(cw.written, r)
 	}
 	if err != nil {
-		glog.Errorf("streamFromVolumeServers: streamFn failed after writing %d bytes: %v", cw.written, err)
+		switch {
+		case errors.Is(err, context.Canceled):
+			// Client disconnected mid-stream (e.g. Nginx upstream timeout, browser cancel) - expected
+			glog.V(3).Infof("streamFromVolumeServers: client disconnected after writing %d bytes: %v", cw.written, err)
+		case errors.Is(err, context.DeadlineExceeded):
+			// Server-side deadline exceeded - unexpected, warrants operator attention
+			glog.Warningf("streamFromVolumeServers: server-side deadline exceeded after writing %d bytes: %v", cw.written, err)
+		default:
+			glog.Errorf("streamFromVolumeServers: streamFn failed after writing %d bytes: %v", cw.written, err)
+		}
 		// Streaming error after WriteHeader was called - response already partially written
 		return newStreamErrorWithResponse(err)
 	}