Fix release review findings in RAR, GZip, and split ZIP parsing

tests/SharpCompress.Test/Mocks/ShortReadStream.cs

@@ -0,0 +1,28 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace SharpCompress.Test.Mocks;
+
+// Exercise legal partial reads through every stream read overload used by the parsers.
+internal sealed class ShortReadStream(Stream stream, int maxReadSize = 1, bool seekable = true)
+    : TestStream(stream, read: true, write: false, seek: seekable)
+{
+    public override int Read(byte[] buffer, int offset, int count) =>
+        base.Read(buffer, offset, Math.Min(count, maxReadSize));
+
+    public override Task<int> ReadAsync(
+        byte[] buffer,
+        int offset,
+        int count,
+        CancellationToken cancellationToken
+    ) => base.ReadAsync(buffer, offset, Math.Min(count, maxReadSize), cancellationToken);
+
+#if !LEGACY_DOTNET
+    public override ValueTask<int> ReadAsync(
+        Memory<byte> buffer,
+        CancellationToken cancellationToken = default
+    ) => base.ReadAsync(buffer.Slice(0, Math.Min(buffer.Length, maxReadSize)), cancellationToken);
+#endif
+}