Fix TarFactory.cs formatting to unblock CI

[Copilot]

The NuGet Release / build-and-publish CI job was failing because CreateNestedRecordingStream and its closing brace were not indented within the class body, causing dotnet csharpier check to exit with code 1.

Changes

• TarFactory.cs: Added two new private helper methods (from PR Tar: Fix memory leak regression #1403) with correct CSharpier-compliant indentation:
  • IsGenuinelySeekable(Stream) — unwraps nested SharpCompressStream layers to check whether the underlying stream genuinely supports Seek
  • CreateNestedRecordingStream(Stream) — returns a SeekableSharpCompressStream for seekable streams (no ring buffer allocation) or a ring-buffered SharpCompressStream for non-seekable streams
• OpenReader: switched from new SharpCompressStream(stream) to CreateNestedRecordingStream(stream), and added sharpCompressStream.Rewind() before StopRecording() so the reader position is reset before handing the stream to TarReader

[Copilot]

Pull request overview

This PR fixes TarFactory.OpenReader to avoid allocating a large rewind ring buffer when the real underlying stream is already seekable, while also ensuring the stream position is rewound before ending the recording scope so TarReader always starts from the correct position. This aligns OpenReader with the already-correct rewind behavior in OpenAsyncReader and unblocks CI formatting checks.

Changes:

• Added IsGenuinelySeekable(Stream) to unwrap nested SharpCompressStream layers before checking true underlying CanSeek.
• Added CreateNestedRecordingStream(Stream) to use SeekableSharpCompressStream for genuinely seekable streams (avoids ring-buffer allocation), otherwise fall back to a ring-buffered SharpCompressStream.
• Updated OpenReader to use the helper and to Rewind() before StopRecording() when a wrapper match succeeds.