Add support for HTTP range requests in DownloadTask

Modified DownloadTask to use HttpRequestMessage with Range headers when resuming downloads. This enables partial downloads to continue from where they left off, improving reliability for interrupted downloads.

Author: JusterZhu

src/c#/GeneralUpdate.Common/Download/DownloadTask.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Threading;
 using System.Threading.Tasks;
 using GeneralUpdate.Common.Shared;
@@ -54,7 +55,14 @@ private async Task DownloadFileRangeAsync(string url, string path)
             {
                 var tempPath = path + ".temp";
                 var startPos = CheckFile(tempPath);
-                using var response = await _httpClient.GetAsync(url, HttpCompletionOption.ResponseHeadersRead);
+                
+                var requestMessage = new HttpRequestMessage(HttpMethod.Get, url);
+                if (startPos > 0)
+                {
+                    requestMessage.Headers.Range = new RangeHeaderValue(startPos, null);
+                }
+                
+                using var response = await _httpClient.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead);
                 if (!response.IsSuccessStatusCode)
                     throw new HttpRequestException($"Failed to download file: {response.ReasonPhrase}");