submodule对gitea不管用，所以直接拉了一份拉格兰

Lagrange.Core/Lagrange.OneBot/Message/SegmentBase.cs

@@ -0,0 +1,13 @@
+using Lagrange.Core.Message;
+using LiteDB;
+
+namespace Lagrange.OneBot.Message;
+
+public abstract class SegmentBase
+{
+    public LiteDatabase? Database { protected get; set; }
+    
+    public abstract void Build(MessageBuilder builder, SegmentBase segment);
+    
+    public abstract SegmentBase? FromEntity(MessageChain chain, IMessageEntity entity);
+}