Add sim parsing for Steam2 sim/sid installers

SabreTools.Data.Models/Steam2Installer/Constants.cs

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+namespace SabreTools.Data.Models.Steam2Installer
+{
+    public static class Constants
+    {
+        public static readonly byte[] SimSignatureBytes = [0x1F, 0x4C, 0xD0, 0x3F];
+
+        /// <remarks>All other values in the structure are little endian, assuming this is too</remarks>
+        public const uint SimSignatureUInt32 = 0x3FD04C1F;
+    }
+}

SabreTools.Data.Models/Steam2Installer/FileEntry.cs

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+using System.Runtime.InteropServices;
+
+namespace SabreTools.Data.Models.Steam2Installer
+{
+
+    public sealed class FileEntry
+    {
+        /// <summary>
+        /// Offset of the filename in the string bytes array
+        /// </summary>
+        public uint NameOffset { get; set; }
+
+        /// <summary>
+        /// Offset of the path name in the string bytes array
+        /// </summary>
+        public uint PathOffset { get; set; }
+
+        /// <summary>
+        /// Steam depot id of the depot the file is a part of
+        /// </summary>
+        public uint DepotId { get; set; }
+
+        /// <summary>
+        /// Offset of the file within its sid volume
+        /// </summary>
+        public ulong Offset { get; set; }
+
+        /// <summary>
+        /// Size of the file, in bytes
+        /// </summary>
+        public ulong Size { get; set; }
+
+        /// <summary>
+        /// Which # installer disc the file is on
+        /// </summary>
+        public byte DiscNumber { get; set; }
+
+        /// <summary>
+        /// Which # sid volume the file is in
+        /// </summary>
+        public byte VolumeNumber { get; set; }
+
+        /// <summary>
+        /// Whether the file is encrypted or not
+        /// </summary>
+        /// <remarks>
+        /// This flag isn't entirely reliable, as sometimes the file is encrypted in the sid without this
+        /// flag being set in the sid. The reverse is not currently known to be true, though, so there at
+        /// least shouldn't be any false positives when using this flag.
+        /// </remarks>
+        public bool Encrypted { get; set; }
+
+        /// <summary>
+        /// Unknown 1-byte value, likely just padding
+        /// </summary>
+        public byte Unknown { get; set; }
+
+        // The filename and path aren't stored in the fileentry structure in the .sim, but the offsets are,
+        // so it just makes sense to also parse and store the strings for the file here too.
+
+        /// <summary>
+        /// The filename
+        /// </summary>
+        public string Name { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The file path
+        /// </summary>
+        public string Path { get; set; } = string.Empty;
+    }
+}

SabreTools.Data.Models/Steam2Installer/Header.cs

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+using System.Runtime.InteropServices;
+
+namespace SabreTools.Data.Models.Steam2Installer
+{
+    /// <summary>
+    /// Header from the .sim file.
+    /// </summary>
+    public sealed class Header
+    {
+        /// <summary>
+        /// .sim file magic value
+        /// </summary>
+        public uint Magic { get; set; }
+
+        /// <summary>
+        /// Version (0x00000001)
+        /// </summary>
+        public uint Version { get; set; }
+
+        /// <summary>
+        /// Number of discs
+        /// </summary>
+        public uint Discs { get; set; }
+
+        /// <summary>
+        /// Size of the section containing file and path strings.
+        /// </summary>
+        public uint StringsSize { get; set; }
+    }
+}

SabreTools.Data.Models/Steam2Installer/SimFile.cs

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+namespace SabreTools.Data.Models.Steam2Installer
+{
+    /// <summary>
+    /// .sim file for a .sim/.sid archive
+    /// </summary>
+    /// <remarks>
+    /// While it is not known for sure what .sim stands for, it's assumed to mean Steam Installer Manifest.
+    /// This contains information about the .sid data volumes. It's used for retail installer discs for
+    /// Steam2 (Steam pre-Steam3/SteamPipe). Preceded by GCF (GCF and NCF are still used for actual game
+    /// installs on Steam2, sim/sid just replaced GCF for retail discs. NCF was never directly stored on
+    /// retail discs since sim/sid had already come out). Succeeded by csm/csd for Steam3/SteamPipe.
+    /// Code is based on NickNine's python-based sim/sid extractor at https://pastebin.com/sj6F64XP
+    /// While this was not referenced for any of the code in SabreTools, https://codeberg.org/CYBERDEV/SIDEx
+    /// provides additional documentation if it is needed.
+    /// </remarks>
+    public sealed class SimFile
+    {
+        /// <summary>
+        /// .sim file header
+        /// </summary>
+        public Header Header { get; set; } = new();
+
+        // The string bytes array would go here, but it gets parsed out into FileEntries during deserialization,
+        // so there's no point storing it in the model. Same with the file entries size and count.
+
+        /// <summary>
+        /// Array of file entries
+        /// </summary>
+        public FileEntry[] FileEntries { get; set; } = [];
+    }
+}

SabreTools.Data.Models/Steam2Installer/Steam2InstallerSet.cs

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+namespace SabreTools.Data.Models.Steam2Installer
+{
+    public class Steam2InstallerSet
+    {
+        /// <summary>
+        /// The sim file
+        /// </summary>
+        public SimFile Sim { get; set; } = new();
+
+        /// <summary>
+        /// The set of sid file volumes
+        /// </summary>
+        // public SidFile[] Sid { get; set; } = [];
+    }
+}

SabreTools.Serialization.Readers.Test/Steam2InstallerTests.cs

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+using System.IO;
+using System.Linq;
+using Xunit;
+
+namespace SabreTools.Serialization.Readers.Test
+{
+    public class Steam2InstallerTests
+    {
+        [Fact]
+        public void NullArray_Null()
+        {
+            byte[]? data = null;
+            int offset = 0;
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data, offset);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void EmptyArray_Null()
+        {
+            byte[]? data = [];
+            int offset = 0;
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data, offset);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void InvalidArray_Null()
+        {
+            byte[]? data = [.. Enumerable.Repeat<byte>(0xFF, 1024)];
+            int offset = 0;
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data, offset);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void NullStream_Null()
+        {
+            Stream? data = null;
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void EmptyStream_Null()
+        {
+            Stream? data = new MemoryStream([]);
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void InvalidStream_Null()
+        {
+            Stream? data = new MemoryStream([.. Enumerable.Repeat<byte>(0xFF, 1024)]);
+            var deserializer = new Steam2Installer();
+
+            var actual = deserializer.Deserialize(data);
+            Assert.Null(actual);
+        }
+    }
+}