Reduce allocations in 7z encryption and codec lookup

tests/SharpCompress.Performance/Benchmarks/SevenZipEncryptionBenchmarks.cs

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+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using BenchmarkDotNet.Attributes;
+using SharpCompress.Common;
+using SharpCompress.Compressors.LZMA;
+using SharpCompress.Writers.SevenZip;
+
+namespace SharpCompress.Performance.Benchmarks;
+
+[MemoryDiagnoser]
+public class SevenZipEncryptionBenchmarks
+{
+    private byte[] inputBytes = null!;
+    private string[] names = null!;
+    private SevenZipWriterOptions options = null!;
+
+    [Params(CompressionType.LZMA, CompressionType.LZMA2)]
+    public CompressionType Codec { get; set; }
+
+    [Params("None", "Data", "DataAndHeader")]
+    public string Encryption { get; set; } = null!;
+
+    [Params(false, true)]
+    public bool ManySmallFiles { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        inputBytes = new byte[ManySmallFiles ? 128 : 262144];
+        new Random(1476).NextBytes(inputBytes);
+        names = new string[ManySmallFiles ? 100 : 1];
+        for (var i = 0; i < names.Length; i++)
+        {
+            names[i] = $"file{i}";
+        }
+        options = new SevenZipWriterOptions(Codec)
+        {
+            Password = Encryption == "None" ? null : "profile",
+            EncryptHeader = Encryption == "DataAndHeader",
+            LeaveStreamOpen = true,
+            LzmaProperties = new LzmaEncoderProperties(true, 4096),
+        };
+    }
+
+    [Benchmark]
+    public long Write()
+    {
+        // Include archive construction/finalization, but avoid output-growth noise.
+        using var output = new MemoryStream(1048576);
+        using (var writer = new SevenZipWriter(output, options))
+        {
+            foreach (var name in names)
+            {
+                using var input = new MemoryStream(inputBytes, writable: false);
+                writer.Write(name, input, null);
+            }
+        }
+        return output.Length;
+    }
+
+    [Benchmark]
+    public async Task<long> WriteAsync()
+    {
+        using var output = new MemoryStream(1048576);
+        await using (var writer = new SevenZipWriter(output, options))
+        {
+            foreach (var name in names)
+            {
+                using var input = new MemoryStream(inputBytes, writable: false);
+                await writer
+                    .WriteAsync(name, input, null, CancellationToken.None)
+                    .ConfigureAwait(false);
+            }
+        }
+        return output.Length;
+    }
+}