Add compression magic number detection to System.Formats.Tar with helpful error messages

[iremyux]

This PR improves the experience of reading compressed tar archives by detecting common compression formats before parsing. It now provides clear, localized messages that explain whether the archive is compressed with a supported format (e.g., GZIP, ZLIB) or an unsupported one (e.g., BZIP2, LZ4, XZ). For supported formats, it guides users to wrap the stream with the right .NET class, and for unsupported formats, it advises decompression first.

Fixes #89056

[Copilot]

Pull Request Overview

This PR enhances the System.Formats.Tar library by adding compression format detection at the beginning of tar archive reading. When users attempt to read a compressed tar file directly without decompression, the library now provides helpful error messages that identify the compression type and guide users on the appropriate solution.

• Adds magic number detection for common compression formats (GZIP, ZLIB, BZIP2, LZ4, XZ, etc.)
• Provides differentiated error messages for supported vs unsupported compression formats
• Integrates compression checking into both synchronous and asynchronous tar reading workflows

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
TarHeader.Read.cs	Adds compression detection logic and calls to check magic numbers during tar header reading
Strings.resx	Adds localized error message templates for supported and unsupported compression detection

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

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[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Read.cs:1

• The new ThrowIfCompressedArchive method lacks test coverage. Consider adding tests for each supported compression format (GZIP, BZIP2, XZ, Zstandard, ZIP, 7-Zip, ZLIB) to verify the detection logic and error messages work correctly. Tests should verify that each compression format's magic number is properly detected and throws the expected InvalidDataException with the correct format name.

// Licensed to the .NET Foundation under one or more agreements.

[Copilot]

The XML doc comment for the exception should use proper XML documentation tags. The <exception> tag should be placed outside the closing </summary> tag and include a proper description with a period at the end.

Suggested change

	/// <exception cref="InvalidDataException">Thrown if a compression format is detected</exception>
	/// </summary>
	/// </summary>
	/// <exception cref="InvalidDataException">Thrown if a compression format is detected.</exception>