Replace 'o' format with 's' format for ISO 8601 dates

Co-authored-by: waldekmastykarz <11164679+waldekmastykarz@users.noreply.github.com>

Author: Copilot

DevProxy.Plugins/Behavior/GraphRandomErrorPlugin.cs

@@ -291,7 +291,7 @@ private void UpdateProxyResponse(ProxyRequestArgs e, HttpStatusCode errorStatus)
         var requestId = Guid.NewGuid().ToString();
         var now = DateTime.Now;
         var requestDateHeader = now.ToString("r", CultureInfo.InvariantCulture);
-        var requestDateInnerError = now.ToString("o", CultureInfo.InvariantCulture);
+        var requestDateInnerError = now.ToString("s", CultureInfo.InvariantCulture);
         var request = session.HttpClient.Request;
         var headers = ProxyUtils.BuildGraphResponseHeaders(request, requestId, requestDateHeader);
         if (errorStatus == HttpStatusCode.TooManyRequests)

DevProxy.Plugins/Behavior/RateLimitingPlugin.cs

@@ -248,7 +248,7 @@ private void UpdateProxyResponse(ProxyHttpEventArgsBase e, HttpStatusCode errorS
                 var requestId = Guid.NewGuid().ToString();
                 var now = DateTime.Now;
                 var requestDateHeader = now.ToString("r", CultureInfo.InvariantCulture);
-                var requestDateInnerError = now.ToString("o", CultureInfo.InvariantCulture);
+                var requestDateInnerError = now.ToString("s", CultureInfo.InvariantCulture);
                 headers.AddRange(ProxyUtils.BuildGraphResponseHeaders(request, requestId, requestDateHeader));
 
                 body = JsonSerializer.Serialize(new GraphErrorResponseBody(

DevProxy.Plugins/Behavior/RetryAfterPlugin.cs

@@ -110,7 +110,7 @@ private static void UpdateProxyResponse(ProxyRequestArgs e, ThrottlingInfo throt
             var requestId = Guid.NewGuid().ToString();
             var now = DateTime.Now;
             var requestDateHeader = now.ToString("r", CultureInfo.InvariantCulture);
-            var requestDateInnerError = now.ToString("o", CultureInfo.InvariantCulture);
+            var requestDateInnerError = now.ToString("s", CultureInfo.InvariantCulture);
             headers.AddRange(ProxyUtils.BuildGraphResponseHeaders(request, requestId, requestDateHeader));
 
             body = JsonSerializer.Serialize(new GraphErrorResponseBody(

DevProxy.Plugins/Generation/HarGeneratorPlugin.cs

@@ -102,7 +102,7 @@ private HarEntry CreateHarEntry(RequestLog log)
 
         var entry = new HarEntry
         {
-            StartedDateTime = currentTime.ToString("o"),
+            StartedDateTime = currentTime.ToString("s"),
             Time = 0, // We don't have actual timing data in RequestLog
             Request = new HarRequest
             {