Single brick shortcut

Add special case handling for when the application requests just a single brick, aligned to brick size, not compressed, file opened read only, no consolidating of cloud bricks (implied by reading brick at a time), not accessing data from Google cloud (only Azure and on-prem), not requested scaled from integral to float.

The list of conditions needed for the tweak to kick in is longer that with the malloc tweak. On the positive side, when it does kick in the effect will very likely be better. Getting measurably better performance might still require "lab conditions".

More details will be added as comments in the pull request.