Add Z3DS file header structure

SabreTools.Data.Models/N3DS/Constants.cs

@@ -22,5 +22,9 @@ namespace SabreTools.Data.Models.N3DS
         public static byte[] RomfsCounter = [0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00];
 
         public const int CXTExtendedDataHeaderLength = 0x800;
+
+        // Z3DS
+
+        public const string Z3DSMagicNumber = "Z3DS";
     }
 }

SabreTools.Data.Models/N3DS/Z3DSFileHeader.cs

@@ -0,0 +1,52 @@
+namespace SabreTools.Data.Models.N3DS
+{
+    /// <summary>
+    /// File header for Zstd-compressed 3DS data
+    /// </summary>
+    /// <see href="https://github.com/azahar-emu/azahar/blob/master/src/common/zstd_compression.h"/>
+    public class Z3DSFileHeader
+    {
+        /// <summary>
+        /// Magic ID, always 'Z3DS'
+        /// </summary>
+        /// <remarks>4 bytes</remarks>
+        public string Magic { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Magic ID of the compressed structure
+        /// </summary>
+        /// <remarks>4 bytes</remarks>
+        public string UnderlyingMagic { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Header version
+        /// </summary>
+        /// <remarks>Currently only a value of 1 is expected</remarks>
+        public byte Version { get; set; }
+
+        /// <summary>
+        /// Reserved
+        /// </summary>
+        public byte Reserved { get; set; }
+
+        /// <summary>
+        /// Header size
+        /// </summary>
+        public ushort HeaderSize { get; set; }
+
+        /// <summary>
+        /// Metadata size
+        /// </summary>
+        public uint MetadataSize { get; set; }
+
+        /// <summary>
+        /// Compressed size of the structure data
+        /// </summary>
+        public ulong CompressedSize { get; set; }
+
+        /// <summary>
+        /// Uncompressed size of the structure data
+        /// </summary>
+        public ulong UncompressedSize { get; set; }
+    }
+}