Update Solution to .NET 9

[StevenTCramer]

Description

Update the solution to use .NET 9, focusing on:

• Updating global.json to target .NET 9
• Updating Directory.Build.props to reference .NET 9
• Resolving any breaking changes from .NET 8 to .NET 9
• Ensuring all projects build successfully with .NET 9

Acceptance Criteria

• Update global.json to target .NET 9
• Update Directory.Build.props to reference .NET 9
• Resolve any breaking changes
• Verify all projects build successfully
• Create follow-up task for utilizing new .NET 9 features

Notes

• This task is only for the migration to .NET 9
• A separate task will be created to utilize new .NET 9 features
• Refer to Microsoft's .NET 9 migration guide for breaking changes

Files to Update

• global.json
• Directory.Build.props
• Any project files that have explicit .NET version references

Testing

• Ensure all tests still pass after migration
• Verify NuGet package builds are successful
• Test sample applications work correctly