customizable packet fragmentation settings (#9597)

* first changes

* fix: use ItemsSource for fragment packets ComboBox so value saves correctly

* feat: add customizable packet fragmentation for Xray-core

- Add fragment settings in Core tab: Packets (dropdown), Length (range), Interval (range), MaxSplit (0-10000)
- Support both 'from-to' (e.g., 50-100) and single value (e.g., 50) formats for Length, Interval, and MaxSplit
- Validation with shortened error message: 'Invalid range format. Use from-to (e.g., 50-100).'
- UI in PopupBox (materialDesign) visible only when EnableFragment is checked
- Only Xray-core supported (Mihomo/sing-box fragment code removed)
- Localization updated for 8 languages

* fix: address 2dust review feedback

- Move FragmentPacketsOptions to Global class
- Remove default values from Fragment4RayItem model (set in ConfigHandler)
- Fix Avalonia bindings: move ItemsSource and SelectedItem to code-behind
- Update ViewModel to use Global.FragmentPacketsOptions
- Remove defaults from model properties

* Adjust ui

---------

Co-authored-by: 2dust <31833384+2dust@users.noreply.github.com>

v2rayN/ServiceLib/Services/CoreConfig/V2ray/V2rayOutboundService.cs

@@ -896,9 +896,17 @@ public partial class CoreConfigV2rayService
 
     private (Mask4Ray tcpFragment, Mask4Ray udpNoise) BuildFragmentsMasks()
     {
-        var configPackets = _config.Fragment4RayItem?.Packets ?? "tlshello";
-        var configLength = _config.Fragment4RayItem?.Length ?? "50-100";
-        var configDelay = _config.Fragment4RayItem?.Interval ?? "10-20";
+        var configPackets = _config.Fragment4RayItem?.Packets.NullIfEmpty() ?? "tlshello";
+        var configLength = _config.Fragment4RayItem?.Length.NullIfEmpty() ?? "50-100";
+        var configDelay = _config.Fragment4RayItem?.Interval.NullIfEmpty() ?? "10-20";
+        var configMaxSplit = _config.Fragment4RayItem?.MaxSplit.NullIfEmpty() ?? "0";
+
+        var maxSplit = 0;
+        var parts = configMaxSplit.Split('-');
+        if (parts.Length > 0 && int.TryParse(parts[0], out var ms))
+        {
+            maxSplit = ms;
+        }
 
         var fragmentMask = new Mask4Ray
         {
@@ -908,6 +916,7 @@ public partial class CoreConfigV2rayService
                 packets = configPackets,
                 length = configLength,
                 delay = configDelay,
+                maxSplit = maxSplit,
             }
         };
         var noiseMask = new Mask4Ray