.NET (OK, C#) finally gets union types

C# 15, coming with .NET 11, is introducing native union type support using a new `union` keyword, allowing developers to create types that can represent multiple different types in a type-safe manner. Union types enable developers to handle data that could be one of several potentially unrelated types (such as different operating systems) and work with them using switch expressions, eliminating the need for workarounds like base classes or object storage. This feature has long been available in functional programming languages like F# and TypeScript but is now natively supported in C#.