Update all projects to .NET 9 and enable multi-targeting for libraries (.NET 8 and .NET 9) #202
Description
Update all projects in the repository to target .NET 9. For library projects, enable multi-targeting so they support both .NET 8 and .NET 9.
Tasks:
- Update project files for applications to target .NET 9
- Update library projects to multi-target .NET 8 and .NET 9
- Update CI/CD pipeline definitions if necessary to test/build on .NET 9
- Update NuGet packages
- Verify compatibility and run all tests
This ensures forward compatibility and helps consumers transition smoothly to .NET 9 while maintaining support for .NET 8.