refactor: rewrite lfs pointer detection and image loading

Signed-off-by: leo <longshuang@msn.cn>

src/Models/ImageDecoder.cs

@@ -0,0 +1,8 @@
+namespace SourceGit.Models
+{
+    public enum ImageDecoder
+    {
+        None = 0,
+        Builtin,
+    }
+}

src/Models/LFSObject.cs

@@ -1,8 +1,22 @@
-namespace SourceGit.Models
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Models
 {
-    public class LFSObject
+    public partial class LFSObject
     {
+        [GeneratedRegex(@"^version https://git-lfs.github.com/spec/v\d+\r?\noid sha256:([0-9a-f]+)\r?\nsize (\d+)[\r\n]*$")]
+        private static partial Regex REG_FORMAT();
+
         public string Oid { get; set; } = string.Empty;
         public long Size { get; set; } = 0;
+
+        public static LFSObject Parse(string content)
+        {
+            var match = REG_FORMAT().Match(content);
+            if (match.Success)
+                return new() { Oid = match.Groups[1].Value, Size = long.Parse(match.Groups[2].Value) };
+
+            return null;
+        }
     }
 }

src/Models/RevisionFile.cs

@@ -1,4 +1,6 @@
-using Avalonia.Media.Imaging;
+using System.Globalization;
+using System.IO;
+using Avalonia.Media.Imaging;
 
 namespace SourceGit.Models
 {
@@ -9,10 +11,17 @@ namespace SourceGit.Models
 
     public class RevisionImageFile
     {
-        public Bitmap Image { get; set; } = null;
-        public long FileSize { get; set; } = 0;
-        public string ImageType { get; set; } = string.Empty;
+        public Bitmap Image { get; }
+        public long FileSize { get; }
+        public string ImageType { get; }
         public string ImageSize => Image != null ? $"{Image.PixelSize.Width} x {Image.PixelSize.Height}" : "0 x 0";
+
+        public RevisionImageFile(string file, Bitmap img, long size)
+        {
+            Image = img;
+            FileSize = size;
+            ImageType = Path.GetExtension(file)!.Substring(1).ToUpper(CultureInfo.CurrentCulture);
+        }
     }
 
     public class RevisionTextFile