Extract buffer_op from delay_op

[khabinov]

No description provided.

[parsifal-47]

what would be the behavior of delay_op in this case:
request -- increase counter if we have our timer scheduled, otherwise request upstream
on_next -- ignore, because we don't have a buffer
on_timer -- request upstream if there where any requests downstream

Because of on_next behavior, it would be unusable without upstream buffer_op.

Do you think it would be useful?

[khabinov]

buffer_op itself might be useful in other places.

[parsifal-47]

ok, am I describing its behavior correctly?
if there is a need for additional discussion -- please let me know