Monad support

[domn1995]

As a developer, I want to use this library to generate monads, so that I don't have to write them manually.

I should be able to do something like this:

[Union]
public partial record Option<T>
{
    partial record Some(T Value);
    partial record None();
}

var option = new Option<string>.Some("foo");

var value = option.Match(
    some => some.Value,
    none => ""
);

Console.WriteLine(value); // "foo"

[Union]
public partial record Result<TFailure, TSuccess>
{
    partial record Success(TSuccess Value);
    partial record Failure(TFailure Error);
}

var result = new Result<Exception, string>.Failure(new Exception("Boom!"));
var message = result.Match(
    success => success.Value,
    failure => failure.Error.Message
);

Console.WriteLine(message); // "Boom!"

[domn1995]

Closed by #24 and #25