Harden Auto* data sources for TUnit 1.66 and add generic attributes

[aivascu]

Summary

Upgrade TUnit and harden Auto* data sources so member/class/method/field/property rows behave more reliably, including class-level (constructor) data. Add generic Auto* attributes, refresh docs and brand assets, and modernize CI/tooling.

Fixes

• Upgrade TUnit to 1.66.8 and align Auto* sources with the current async data-source model
• Share row conversion (ToAsyncDataRows) across member, class, method, field, and property sources
• Guard null and excess-length data rows instead of failing in unclear ways
• Match class-level ClassParameters to the constructor TUnit actually uses (DataGeneratorMetadataExtensions)
• Pin net48 test builds to AnyCPU so the Framework SDK does not default to win-x86

Features

• Generic attributes (C# 11+): [AutoClassDataSource<T>], [AutoMemberDataSource<T>], [AutoArguments<T>]
• Document supported member/class data-source result shapes in the README
• Broader public-API coverage for shapes, class-level scenarios, and generic usage
• NuGet/IDE package readme under assets/readme.md, plus CONTRIBUTING notes and AutoFixture brand assets

Tooling

• Harden Nuke/CI for net8.0 / net10.0, simplify analyzer setup for tests
• Bump GitHub Actions to checkout@v7, setup-dotnet@v6, cache@v6, and upload-artifact@v7
• Prefer collection expressions where the target type is clear