Remove multi-value overloads

Methods writing an enumerable of items clutter the list of overloads more than they are adding to useful functionality.

Also, async multi-instance overloads do not throw in the foreach overload if a cancellation was requested. This would have to be added to every single overload of them.

The amount of overloads created by them (together with the upcoming out overloads) is just not worth keeping them as they make the library unmaintainable and error-prone to extension.

Instead, ensure Read/WriteMany(Async) overloads are working as expected (like, adding the cancellation throw there in one place).