House keeping

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[Copilot]

Pull Request Overview

This is a housekeeping PR focused on updating dependencies, modernizing code practices, and streamlining the build process. The changes include package updates, dependency migrations, and workflow improvements.

• Updated multiple NuGet packages to newer versions across test and main projects
• Migrated from SixLabors.ImageSharp to SkiaSharp for image processing
• Improved code quality with better documentation, error handling, and class design

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
OpenXmlToHtmlTests/OpenXmlToHtmlTests.csproj	Updated test SDK and analyzer packages
OpenXmlToHtmlTests/OpenXmlToHtmlIntegrationTests.cs	Migrated from ImageSharp to SkiaSharp for bitmap validation
OpenXmlToHtmlOpenApiTests/OpenXmlToHtmlOpenApiTests.csproj	Updated AngleSharp, test SDK, and test runner packages
OpenXmlToHtmlCli/Program.cs	Made Program class static since it only contains static methods
OpenXmlToHtmlCli/OpenXmlToHtmlCli.csproj	Updated SonarAnalyzer and ILLink packages
OpenXmlToHtml/Tooling/Linux.cs	Added XML documentation and made class static with better exception handling
OpenXmlToHtml/OpenXmlToHtml.csproj	Updated OpenXmlPowerTools and SonarAnalyzer packages
OpenXmlToHtml/ExportImageHandler.cs	Added input validation and improved null checking
.vscode/settings.json	Added test discovery configuration
.github/workflows/dotnet.yml	Replaced third-party zip action with native PowerShell command and removed Azure deployment job

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