Closes: 9016

The new benchmark test for blobs fs backend was rebased from a merge
request in which it was written using the new interface for blobs
backend. After rebase, the test was not reverted to old interface, and
was just failing bad. This commit fixes it.

-- Closes: #9004

It was generating spaces, causing split to fail sometimes.

Adds a CooperativeTask to stream blobs to client as the transport is
able to handle it, pausing and resuming as necessary.

-- Related: #8809

First version, still missing consumer/producer model and some tweaks,
but working.

-- Related: #8809

-- Related: #8809