submodule对gitea不管用，所以直接拉了一份拉格兰

Lagrange.Core/Lagrange.OneBot/Message/Entity/FileSegment.cs

@@ -0,0 +1,45 @@
+using System.Text.Json.Serialization;
+using Lagrange.Core.Message;
+using Lagrange.Core.Message.Entity;
+
+namespace Lagrange.OneBot.Message.Entity;
+
+[Serializable]
+public partial class FileSegment(string fileName, string fileHash, string fileId, string url)
+{
+    public FileSegment() : this("", "", "", "") { }
+    
+    [JsonPropertyName("file_name")] public string Filename { get; set; } = fileName;
+    
+    [JsonPropertyName("file_hash")] public string Filehash { get; set; }  = fileHash;
+
+    [JsonPropertyName("file_id")] public string Fileid { get; set; } = fileId;
+
+    [JsonPropertyName("url")] public string Url { get; set; } = url;
+    
+}
+
+[SegmentSubscriber(typeof(FileEntity), "file")]
+public partial class FileSegment : SegmentBase
+{
+    public override void Build(MessageBuilder builder, SegmentBase segment)
+    {
+        if (segment is FileSegment fileSegment and not { Fileid: "" })
+        {
+            builder.Add(new FileEntity
+            {
+                FileName = fileSegment.Filename,
+                FileUrl = fileSegment.Url,
+                FileId = fileSegment.Fileid,
+                FileHash = fileSegment.Filehash
+            });
+        }
+    }
+
+    public override SegmentBase FromEntity(MessageChain chain, IMessageEntity entity)
+    {
+        if (entity is not FileEntity fileEntity) throw new ArgumentException("Invalid entity type.");
+
+        return new FileSegment(fileEntity.FileName, fileEntity.FileHash ?? "", fileEntity.FileId ?? fileEntity.FileUuid ??  "", fileEntity.FileUrl ?? "");
+    }
+}