add AOT smoke and missing tests

tests/SharpCompress.AotSmoke/Program.cs

@@ -0,0 +1,59 @@
+using System;
+using System.IO;
+using System.Text;
+using SharpCompress.Archives;
+using SharpCompress.Common;
+using SharpCompress.Readers;
+using SharpCompress.Writers;
+
+var original = "SharpCompress AOT smoke test";
+using var archiveStream = new MemoryStream();
+
+using (
+    var writer = WriterFactory.OpenWriter(
+        archiveStream,
+        ArchiveType.Zip,
+        new WriterOptions(CompressionType.Deflate) { LeaveStreamOpen = true }
+    )
+)
+{
+    using var entryStream = new MemoryStream(Encoding.UTF8.GetBytes(original));
+    writer.Write("payload.txt", entryStream, DateTime.UtcNow);
+}
+
+archiveStream.Position = 0;
+using (var reader = ReaderFactory.OpenReader(archiveStream, ReaderOptions.ForExternalStream))
+{
+    if (!reader.MoveToNextEntry() || reader.Entry.IsDirectory)
+    {
+        throw new InvalidOperationException("Expected a file entry.");
+    }
+
+    using var extracted = new MemoryStream();
+    reader.WriteEntryTo(extracted);
+    var actual = Encoding.UTF8.GetString(extracted.ToArray());
+    if (!string.Equals(original, actual, StringComparison.Ordinal))
+    {
+        throw new InvalidOperationException("ReaderFactory round-trip content mismatch.");
+    }
+}
+
+archiveStream.Position = 0;
+using (var archive = ArchiveFactory.OpenArchive(archiveStream, ReaderOptions.ForExternalStream))
+{
+    var entryCount = 0;
+    foreach (var entry in archive.Entries)
+    {
+        if (!entry.IsDirectory)
+        {
+            entryCount++;
+        }
+    }
+
+    if (entryCount != 1)
+    {
+        throw new InvalidOperationException("ArchiveFactory did not see the expected entry.");
+    }
+}
+
+Console.WriteLine("SharpCompress AOT smoke test passed.");