Fix critical bug with nested property injection and data source caching (#2768)

The source generator was incorrectly bypassing data source attribute logic by
directly instantiating objects. This broke important features like caching
and reuse in ClassDataSourceAttribute.

Changes:
- Remove all direct instantiation logic from DataSourceHelpersGenerator
- Delegate all property resolution to DataSourceHelpers.ResolveDataSourceForPropertyAsync
- Ensure data source attributes maintain full control over instance creation
- Fix value type comparisons for .NET Framework compatibility
- Simplify generator to only call GetDataRowsAsync on IDataSourceAttribute

This ensures that SharedType settings (PerClass, PerTestSession, etc.) work
correctly and nested property injection respects the data source logic.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: thomhurst