Removed wrappers that weren't needed (probably)

[adamhathcock]

Found while doing #958

[Copilot]

Pull Request Overview

This PR removes wrapper usage by replacing SharpCompressStream.Create(stream, leaveOpen: true) with direct stream usage in BinaryReader constructors across XZ compression components.

• Simplified BinaryReader instantiation by removing SharpCompressStream wrapper
• Updated three XZ component classes to use direct stream access
• Maintained the same leaveOpen behavior using BinaryReader's leaveOpen parameter

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/SharpCompress/Compressors/Xz/XZIndex.cs	Removed SharpCompressStream wrapper in FromStream method
src/SharpCompress/Compressors/Xz/XZHeader.cs	Removed SharpCompressStream wrapper in FromStream method
src/SharpCompress/Compressors/Xz/XZFooter.cs	Removed SharpCompressStream wrapper in FromStream method

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