let xor crypto engine use smart buffers
let xor crypto engine use smart buffers

also use similar buffer strategies to the (tls) crypto codec adapter
to make benchmark comparisons more reasonable.

vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa