AST-1294 Switch StationAdder::process to XTensor DPBuffer interface

Malcolm MacLeodrequested to merge
ast-1294-stationadder-use-uniqueptr into master

Adapt StationAdder to use unique DPBuffer pointer interface and XTensor view Adapt the bulk of one of the tStationAdder unit tests to use unique DPBuffer pointer interface and XTensor view

Edited by Malcolm MacLeod

Merge request reports