fix: set HttpClient.Timeout to infinite to honor per-request cancellation

HttpClient.Timeout defaults to ~100s and would cap requests before a
caller-configured DownloadTimeout takes effect. Setting it to infinite
lets HttpDownloadExecutor and VersionService per-request
CancellationTokenSource.CancelAfter control timeout precisely.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: JusterZhu

src/c#/GeneralUpdate.Core/Network/HttpClientProvider.cs

@@ -32,7 +32,14 @@ static HttpClientProvider()
         var handler = new HttpClientHandler();
         handler.ServerCertificateCustomValidationCallback = (req, cert, chain, errors) =>
             _sslPolicy.ValidateCertificate(cert, chain, errors);
-        _shared = new HttpClient(handler, disposeHandler: false);
+        _shared = new HttpClient(handler, disposeHandler: false)
+        {
+            // Let per-request CancellationTokenSource.CancelAfter (set by
+            // HttpDownloadExecutor & VersionService) control timeout — the
+            // global HttpClient.Timeout (default ~100s) would otherwise cap
+            // requests before a caller-configured longer DownloadTimeout.
+            Timeout = System.Threading.Timeout.InfiniteTimeSpan
+        };
     }
 
     /// <summary>