Update all samples to .NET 7

[christiannagel]

Part 1 (The Language)

• [x] Chapter 1 - .NET Applications and Tools (HelloWorld)
• [x] Chapter 2 - Core C# (CoreCsharp)
• [x] Chapter 3 - Classes, Structs, Tuples, and Records (Types)
• [x] Chapter 4 - Object-Oriented Programming with C# (ObjectOrientation)
• [x] Chapter 5 - Operators and Casts (OperatorsAndCasts)
• [x] Chapter 6 - Arrays (Arrays)
• [x] Chapter 7 - Delegates, Lambdas, and Events (Delegates)
• [x] Chapter 8 - Collections (Collections)
• [x] Chapter 9 - Language Integrated Query (LINQ)
• [x] Chapter 10 - Errors and Exceptions (ErrorsAndExceptions)
• [x] Chapter 11 - Tasks and Asynchronous Programming (Async)
• [x] Chapter 12 - Reflection, Metadata, and Source Generators (ReflectionAndSourceGenerators)
• [x] Chapter 13 - Managed and Unmanaged Memory (Memory)

Part 2 (The Libraries)

• [x] Chapter 14 - Libraries, Assemblies, Packages, and NuGet (Libraries)
• [x] Chapter 15 - Dependency Injection and Configuration (DependencyInjectionAndConfiguration)
• [ ] Chapter 16 - Diagnostics and Metrics (LoggingAndMetrics)
• [x] Chapter 17 - Parallel Programming (Parallel)
• [x] Chapter 18 - Files and Streams (FilesAndStreams)
• [x] Chapter 19 - Networking (Networking)
• [x] Chapter 20 - Security (Security)
• [x] Chapter 21 - Entity Framework Core (EFCore)
• [x] Chapter 22 - Localization (Localization)
• [x] Chapter 23 - Tests (Tests)

Part 3 (Web Apps and Services)

• [x] Chapter 24 - ASP.NET Core (AspNetCore)
• [ ] Chapter 25 - Services (Services)
• [x] Chapter 26 - Razor Pages and MVC (RazorAndMVC)
• [ ] Chapter 27 - Blazor (Blazor)
• [x] Chapter 28 - SignalR (SignalR)

Part 4 (Windows Apps)

• [x] Chapter 29 - Windows Apps
• [x] Chapter 30 - Patterns with XAML Apps
• [x] Chapter 31 - Styling Windows Apps