submodule对gitea不管用，所以直接拉了一份拉格兰

Lagrange.Core/Lagrange.OneBot/Utility/DateTimeExt.cs

@@ -0,0 +1,10 @@
+using System.Runtime.CompilerServices;
+
+namespace Lagrange.OneBot.Utility;
+
+public static class DateTimeExt
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static uint ToTimestamp(this DateTime time) => 
+        (uint)(time - new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc)).TotalSeconds;
+}