fix: Resolve streaming bug in MemoryWebClient (#959)

Improve web client streaming performance

Author: westdavidr

clients/dotnet/WebClient/MemoryWebClient.cs

@@ -368,7 +368,13 @@ public async IAsyncEnumerable<MemoryAnswer> AskStreamingAsync(
         using StringContent content = new(JsonSerializer.Serialize(request), Encoding.UTF8, "application/json");
 
         var url = Constants.HttpAskEndpoint.CleanUrlPath();
-        HttpResponseMessage response = await this._client.PostAsync(url, content, cancellationToken).ConfigureAwait(false);
+        using var requestMessage = new HttpRequestMessage(HttpMethod.Post, url);
+        requestMessage.Content = content;
+        HttpCompletionOption completionOption = useStreaming
+            ? HttpCompletionOption.ResponseHeadersRead
+            : HttpCompletionOption.ResponseContentRead;
+
+        HttpResponseMessage response = await this._client.SendAsync(requestMessage, completionOption, cancellationToken).ConfigureAwait(false);
         response.EnsureSuccessStatusCode();
 
         if (useStreaming)