Update the solution to use .NET 10 across the board.

• Update build props to use net10
• Update GitHub actions to use net10
• Update to latest version of Aspire
• Update README with version information
• Update all package dependencies to latest version
• Swap out MediatR for Mediator SourceGen
• Bring in changes from sample app (Vogen, behaviors, etc)
• Add more tests
• Make aspire the default, not opt-in