Use invariant culture for AWS date formatting

Updated date formatting and parsing in AWS authentication to explicitly use System.Globalization.CultureInfo.InvariantCulture and DateTimeStyles.AssumeUniversal. This ensures consistent behavior regardless of system locale.

Closes BLD-298

Author: 0xFirekeeper

Thirdweb/Thirdweb.Wallets/InAppWallet/EmbeddedWallet.Authentication/AWS.cs

@@ -132,8 +132,8 @@ private static async Task<string> PostAwsRequestWithDateOverride(
 
         var dateTimeNow = dateOverride ?? DateTime.UtcNow;
         var amzDateFormat = "yyyyMMddTHHmmssZ";
-        var amzDate = dateTimeNow.ToString(amzDateFormat);
-        var dateStamp = dateTimeNow.ToString("yyyyMMdd");
+        var amzDate = dateTimeNow.ToString(amzDateFormat, System.Globalization.CultureInfo.InvariantCulture);
+        var dateStamp = dateTimeNow.ToString("yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);
 
         var canonicalHeaders = $"host:{new Uri(endpoint).Host}\n" + $"x-amz-date:{amzDate}\n";
         var signedHeaders = "host;x-amz-date";
@@ -181,7 +181,7 @@ private static async Task<string> PostAwsRequestWithDateOverride(
                 if (idx > -1)
                 {
                     var parsedTimeString = responseContent.Substring(idx + 1, amzDate.Length);
-                    var serverTime = DateTime.ParseExact(parsedTimeString, amzDateFormat, System.Globalization.CultureInfo.InvariantCulture).ToUniversalTime();
+                    var serverTime = DateTime.ParseExact(parsedTimeString, amzDateFormat, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.AssumeUniversal);
 
                     return await PostAwsRequestWithDateOverride(
                             credentials,