Adding IAsyncDisposable to ViewModels

Any possibility of implementing [IAsyncDisposable](https://learn.microsoft.com/en-us/dotnet/api/system.iasyncdisposable?view=net-7.0) for ViewModels?

I'm using the `Dispose` method as my main way of detecting a user disconnect as recommend in #151, but I have some async work I need to do during that method. It would be great to have the option of overriding `DisposeAsync` to handle this.