perf: replace manual hex formatting with Convert.ToHexStringLower (#2453)

Author: IconHHw

src/Models/AvatarManager.cs

@@ -224,10 +224,7 @@ private string GetEmailHash(string email)
         {
             var lowered = email.ToLower(CultureInfo.CurrentCulture).Trim();
             var hash = MD5.HashData(Encoding.Default.GetBytes(lowered));
-            var builder = new StringBuilder(hash.Length * 2);
-            foreach (var c in hash)
-                builder.Append(c.ToString("x2"));
-            return builder.ToString();
+            return Convert.ToHexStringLower(hash);
         }
 
         private void NotifyResourceChanged(string email, Bitmap image)

src/Models/RepositorySettings.cs

@@ -171,10 +171,7 @@ public void MoveCustomActionDown(CustomAction act)
         private static string HashContent(string source)
         {
             var hash = MD5.HashData(Encoding.Default.GetBytes(source));
-            var builder = new StringBuilder(hash.Length * 2);
-            foreach (var c in hash)
-                builder.Append(c.ToString("x2"));
-            return builder.ToString();
+            return Convert.ToHexStringLower(hash);
         }
 
         private static Dictionary<string, RepositorySettings> _cache = new();