Implement co_await operator for single yaclib::Future

[MBkkt]

First of feel free to ask me(@MBkkt) any questions about this task, often the task may not be described in enough detail for devs who don't have the full context.

Implement co_await operator, for single future, that consume future by rvalue reference and await it (yaclib::Await) and return result from it in await_resume

Now we need to write something like this:

  yaclib::Future<int> f = ...;
  co_await Await(f);
  co_return std::move(f).Touch/Get();

We want to make operators to simplify it:

template<typename T>
yaclib::Result<T> operator co_await(yaclib::Future<T>&&);
template<typename T>
yaclib::Result<T> operator co_await(yaclib::FutureOn<T>&&);

If we will have it, we can write:

  yaclib::Future<int> f = ...;
  co_return co_await std::move(f);