Prefer memory overloads for Stream.ReadAsync/WriteAsync

[turbedi]

Benefits from the returning type being ValueTask<int>.

[bdach]

Have you benchmarked this? What are the measurable performance gains from these changes?

From what I can see from the docs using ValueTask<T> instead of Task<T> is not an automatically free optimisation.

[turbedi]

I haven't done any benchmarks yet, I should be able to do some this weekend.

As far as I understood, it should be a free optimization in cases where where Stream.Read/WriteAsync methods are used.

[peppy]

These are seldom used paths and the operation performed inside the task is magnitudes more intensive than creating a Task instance. I'd be wary of making this change just because-we-can in one location – I may think differently if this was applied along with a performance rule on inspectcode or roslyn to ensure these changes are made anywhere/everywhere.