Update .NET to 9.0 and all dependencies to latest versions

[Copilot]

Overview

This PR updates the project from .NET 6.0 (which is out of support) to .NET 9.0 (the latest stable version) and updates all NuGet package dependencies to their latest compatible versions.

Motivation

.NET 6.0 reached end-of-support and is no longer receiving security updates. The build was generating warnings:

warning NETSDK1138: The target framework 'net6.0' is out of support and will not receive 
security updates in the future. Please refer to https://aka.ms/dotnet-core-support for 
more information about the support policy.

Additionally, several packages were multiple major versions behind their latest releases.

Changes Made

.NET Framework

• Updated from: .NET 6.0 → to: .NET 9.0
• Updated global.json SDK version from 3.1.0 to 9.0.0
• Updated all project TargetFramework properties from net6.0 to net9.0

Package Updates

Entity Framework Core (7.0.4 → 9.0.9)

• Microsoft.EntityFrameworkCore
• Microsoft.EntityFrameworkCore.Relational
• Microsoft.EntityFrameworkCore.SqlServer
• Microsoft.EntityFrameworkCore.Tools
• Microsoft.EntityFrameworkCore.InMemory

Development Tools

• Microsoft.VisualStudio.Web.CodeGeneration.Design: 6.0.13 → 9.0.0

Testing Packages

• Microsoft.NET.Test.Sdk: 17.5.0 → 17.12.0
• MSTest.TestAdapter: 3.0.2 → 3.7.0
• MSTest.TestFramework: 3.0.2 → 3.7.0
• Moq: 4.18.4 → 4.20.72
• coverlet.collector: 3.2.0 → 6.0.2

Note: EntityFrameworkCoreMock.Moq remains at 2.4.0 as it continues to work correctly with the updated EF Core version and all tests pass.

Testing

✅ All 20 existing tests pass successfully:

• UnitTestingDemo.Services.Tests: 4 tests passed
• UnitTestingDemo.Tests: 3 tests passed
• UnitTestingDemo.Data.Tests: 13 tests passed

✅ Build completes successfully with 0 warnings and 0 errors in both Debug and Release configurations.

Impact

• Security: Project now runs on a supported .NET version receiving active security updates
• Performance: Benefits from .NET 9.0 performance improvements
• Compatibility: All dependencies are current and compatible
• Breaking Changes: None - this is a purely infrastructure update with no code changes required

Files Modified

Total: 8 files changed, 30 insertions(+), 30 deletions(-)

• global.json
• src/UnitTestingDemo/UnitTestingDemo.csproj
• src/UnitTestingDemo.Data/UnitTestingDemo.Data.csproj
• src/UnitTestingDemo.Services/UnitTestingDemo.Services.csproj
• src/UnitTestingDemo.Domain/UnitTestingDemo.Domain.csproj
• tests/UnitTestingDemo.Tests/UnitTestingDemo.Tests.csproj
• tests/UnitTestingDemo.Data.Tests/UnitTestingDemo.Data.Tests.csproj
• tests/UnitTestingDemo.Services.Tests/UnitTestingDemo.Services.Tests.csproj

Closes #[issue_number]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Update Dependencies</issue_title>
<issue_description>Update all packages and dependencies. Take .NET to the latest version.
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #12

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