use `ValueTask` instead of `Task` if possible

[MarcoRossignoli]

For compat reason we're returning from the API Tasks we could have some performance benefit (expecially for the IMessageBus IDataConsumer) if we move it to ValueTask.

[Evangelink]

Are you thinking of multi-tfm code or dropping netstandard 2.0?

[MarcoRossignoli]

Are you thinking of multi-tfm code or dropping netstandard 2.0?

We won't never drop netstandard2.0 so or we take a dep there with ValueTask from official package(https://www.nuget.org/packages/System.Threading.Tasks.Extensions/) or #ifdef.

[Youssef1313]

How common it is that APIs in question will complete synchronously? Do we have that data?

[MarcoRossignoli]

How common it is that APIs in question will complete synchronously? Do we have that data?

We don't have info about it, also it's not easy, vast majority of time code run sync but depends on the machine load, CI are not big machines and usually busy so the decision to provide async everywhere.
For the APIs in question we meant all extensions interfaces.