Add Opera FileSystem support (#90)

* Add Opera FileSystem support

* Fix tests

SabreTools.Data.Models/OperaFS/FileSystem.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+
+namespace SabreTools.Data.Models.OperaFS
+{
+    /// <summary>
+    /// Opera Filesystem (or user-data-only disc image) present on 3DO and M2 discs
+    /// Usually contained within a CDROM disc image (2352-byte bin file)
+    /// All fields are Big-Endian
+    /// </summary>
+    /// <see href="https://groups.google.com/g/rec.games.video.3do/c/1U3qrmLSYMQ"/>
+    public sealed class FileSystem
+    {
+        /// <summary>
+        /// Volume Descriptor
+        /// </summary>
+        public VolumeDescriptor VolumeDescriptor { get; set; } = new();
+
+        /// <summary>
+        /// Map of all directories in filesystem, and their offsets
+        /// Duplicate directories exist at different offsets
+        /// </summary>
+        public Dictionary<uint, DirectoryDescriptor> Directories { get; set; } = [];
+    }
+}