refactor process handler, and make a PipeState pydantic basemodel object

[fredrikt]

trafficstars

[coveralls]

Coverage decreased (-0.02%) to 72.009% when pulling 1763776ea64c1b3ffdb238c41ef62be689d923a4 on ft-refactor_process_handler into 052c5561657348a85b099516bbbe8af8affab023 on master.