rework dependencies to be correct for frameworks and update

[adamhathcock]

No description provided.

[Copilot]

Pull Request Overview

This PR updates NuGet package dependencies across the SharpCompress project, focusing on version bumps for testing and runtime packages. The primary goal is to ensure correct framework-specific dependencies while upgrading to newer package versions.

• Updated Microsoft.NET.Test.Sdk from 17.13.0 to 18.0.0
• Bumped System.Buffers from 4.6.0 to 4.6.1 and System.Memory from 4.6.0 to 4.6.3
• Restructured SharpCompress.csproj to apply dependencies conditionally based on target framework

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/SharpCompress.Test/packages.lock.json	Updated test SDK and transitive dependencies to newer versions
src/SharpCompress/packages.lock.json	Updated package versions and reorganized framework-specific dependency entries
src/SharpCompress/SharpCompress.csproj	Moved System.Buffers to framework-conditional ItemGroup and added framework-specific dependencies
Directory.Packages.props	Updated centrally managed package versions for System.Buffers, System.Memory, and test SDK

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