ModApi.UpdateManager: increase buffer size in DownloadClient to 4096

This matches .NET's default buffer size:
https://github.com/microsoft/referencesource/blob/f7df9e2399ecd273e90908ac11caf1433e142448/mscorlib/system/io/filestream.cs#L398

Author: Rosalie241

ModApi.UpdateManager/DownloadClient.cs

@@ -18,7 +18,7 @@ private void copyStreamWithProgress(Stream inputStrem, Stream outputStream)
         {
             long streamLength = inputStrem.Length;
             long totalBytesRead = 0;
-            byte[] buffer = new byte[1024];
+            byte[] buffer = new byte[4096];
             int bytesRead = 0;
             int percentageDownloaded = 0;
             int percentage;