Adds a fixed size buffer in the flow that allows to store elements from a faster upstream until it becomes full. Depending on the defined OverflowStrategy it might drop elements or backpressure the upstream if there is no space available

Emits when downstream stops backpressuring and there is a pending element in the buffer

Backpressures when depending on OverflowStrategy

* Backpressure - backpressures when buffer is full

* DropHead, DropTail, DropBuffer - never backpressures

* Fail - fails the stream if buffer gets full

Completes when upstream completes and buffered elements has been drained

Cancels when downstream cancels

public static Source<TOut, TMat> Buffer<TOut, TMat>(
	this Source<TOut, TMat> flow,
	int size,
	OverflowStrategy strategy
)

[<ExtensionAttribute>]
static member Buffer : 
        flow : Source<'TOut, 'TMat> * 
        size : int * 
        strategy : OverflowStrategy -> Source<'TOut, 'TMat>