server: increase timeout in stall detection from 5s to 30s (#8831)

In some cases, downloads slow due to disk i/o or other factors,
causing the download to restart a part. This causes the download
to "reverse" in percent completion. By increasing the timeout to 30s,
this should happen less frequently.

server/download.go

@@ -368,7 +368,7 @@ func (b *blobDownload) downloadChunk(ctx context.Context, requestURL *url.URL, w
 				lastUpdated := part.lastUpdated
 				part.lastUpdatedMu.Unlock()
 
-				if !lastUpdated.IsZero() && time.Since(lastUpdated) > 5*time.Second {
+				if !lastUpdated.IsZero() && time.Since(lastUpdated) > 30*time.Second {
 					const msg = "%s part %d stalled; retrying. If this persists, press ctrl-c to exit, then 'ollama pull' to find a faster connection."
 					slog.Info(fmt.Sprintf(msg, b.Digest[7:19], part.N))
 					// reset last updated