Prepare dotnet-inspect 0.8.0

[richlander]

Summary

• bump dotnet-inspect to 0.8.0 and refresh release notes
• add --count for a single selected table section
• rewrite README/SKILL around capabilities and workflows, and update docs/workflows for current commands
• serialize CoreCache-dependent tests to avoid cache races

Validation

• dotnet run --project src/dotnet-inspect.Tests -c Release
• dotnet run --project src/DotnetInspector.Services.Tests -c Release
• find docs/workflows -name "*.md" -print0 | xargs -0 npx --yes markdownlint-cli
• npx --yes markdownlint-cli README.md skills/dotnet-inspect/SKILL.md src/dotnet-inspect/release-notes.md
• dotnet run --project src/dotnet-inspect -- System.Text.Json -S "Async*" --count
• dotnet run --project src/dotnet-inspect -- --version