Replace IsLzma2 flag with CompressionType enum for 7z writer API consistency

src/SharpCompress/Common/CompressionType.cs

@@ -9,6 +9,7 @@ public enum CompressionType
     Deflate,
     Rar,
     LZMA,
+    LZMA2,
     BCJ,
     BCJ2,
     LZip,

src/SharpCompress/Writers/SevenZip/SevenZipWriter.cs

@@ -74,14 +74,6 @@ public partial class SevenZipWriter : AbstractWriter
         }
 
         // Compress file data to output stream
-        // TODO: LZMA2 encoding is not yet implemented in SharpCompress's LzmaStream
-        if (sevenZipOptions.IsLzma2)
-        {
-            throw new ArchiveOperationException(
-                "LZMA2 encoding is not yet implemented. Use LZMA (IsLzma2 = false) instead."
-            );
-        }
-
         var compressor = new SevenZipStreamsCompressor(OutputStream.NotNull());
         var packed = compressor.Compress(
             progressStream,

src/SharpCompress/Writers/SevenZip/SevenZipWriterOptions.cs

@@ -15,12 +15,22 @@ public sealed record SevenZipWriterOptions : IWriterOptions
     private int _compressionLevel;
 
     /// <summary>
-    /// The compression type to use. Supported: LZMA (default), LZMA2 (via CompressionType.LZMA with IsLzma2=true).
+    /// The compression type to use. Only LZMA is supported in this version.
     /// </summary>
     public CompressionType CompressionType
     {
         get => _compressionType;
-        init => _compressionType = value;
+        init
+        {
+            if (value != CompressionType.LZMA)
+            {
+                throw new ArgumentException(
+                    $"SevenZipWriter only supports CompressionType.LZMA. Got: {value}",
+                    nameof(value)
+                );
+            }
+            _compressionType = value;
+        }
     }
 
     /// <summary>
@@ -54,11 +64,6 @@ public sealed record SevenZipWriterOptions : IWriterOptions
     public CompressionProviderRegistry Providers { get; init; } =
         CompressionProviderRegistry.Default;
 
-    /// <summary>
-    /// Whether to use LZMA2 instead of LZMA. Default is false (LZMA).
-    /// </summary>
-    public bool IsLzma2 { get; init; }
-
     /// <summary>
     /// Whether to compress the archive header itself using LZMA.
     /// Default is true, matching standard 7-Zip behavior.

tests/SharpCompress.Test/SevenZip/SevenZipWriterTests.cs

@@ -162,15 +162,9 @@ public class SevenZipWriterTests : TestBase
     [Fact]
     public void SevenZipWriter_LZMA2_ThrowsNotSupported()
     {
-        // LZMA2 encoding is not yet implemented in SharpCompress's LzmaStream
-        using var archiveStream = new MemoryStream();
-        using var writer = new SevenZipWriter(
-            archiveStream,
-            new SevenZipWriterOptions { IsLzma2 = true }
+        Assert.Throws<ArgumentException>(
+            () => new SevenZipWriterOptions(CompressionType.LZMA2)
         );
-
-        using var source = new MemoryStream("test"u8.ToArray());
-        Assert.Throws<ArchiveOperationException>(() => writer.Write("test.txt", source, DateTime.UtcNow));
     }
 
     [Fact]