alt Hacker NewsC# isnt a duck type language (well, you can do that via dynamic keyword, but I don't know who would do that typically).
Most integration libraries in Nuget (aka c#'s cargo) are AB type libraries.
E.g. DI Container: Autofac Messaging Library: MediatR Integration: MediatR.Extensions.Autofac.DependencyInjection
There are many examples of popular libraries like this in that world.
C# does not support adding interfaces to foreign types. It does support extension classes to add methods and properties to a type, but nothing that adds fields or changes the list of interfaces implemented by a type. Rust supports this as well, because you can use traits this way.
Dependency injection is a popular solution for this problem, and you can do that as well in Rust. It requires (again) that the API is designed for dependency injection, and instead of interfaces and is-a relationships, you now have "factories" producing the implementation.